Basic difference - in an RTS, you act as a general - you give your (very simple) units a task, and they basically complete it on their own.
In an RPG, you ARE the character. You move them where you want them to go, and control their actions. The best allow you to control (certain) actions right down to what words they say in certain scenes.
This is far from cosmetic.
RTS, RPG, and FPS are not the only categories there are. They’re just the only ones with acronyms. Turn-based strategies (TBS?), simulations, adventure games, wargames, and sports games come to mind.
The required ingredients of the acronym-ed game types-
RPG- Some sort of development of the character(s) you control. Ability to get new equipment, gain HP/mana, learn new spells, etc.
RTS- Can’t be turn-based, you must be able to produce new units you can control. Resource collection is common but not necessary.
FPS- First person interface, primarily action-oriented. The primary focus can’t be puzzle solving or exploration.
There are overlaps and grey areas. I Am Not a Game Reviewer.
When I say that a genuine RPG involves role-play interaction, I do not mean to disparage what I call “imitation RPGs”. However defining Final Fantasy as anything to do with role-playing is futile. That is why I call them imitation RPGS, because they evolved from the classic pen, paper, dice, social games, but they lost the high level of interpersonal interaction the old games used to have. In the future we will see the evolution of these imitation RPGs into a truly role-playing experience, but that is still a few years away.
I expect that these games will incorporate the multi-player environment and the high expression level of MUDs with the technology of existing imitation RPGs (graphics, speed, etc), and they will probably be in the first person perspective. There are some prototypes today, but nothing I have seen which indicates the new genre is already born.
Back to the present, there are good and bad imitation RPGs. Final Fantasy I consider a poor game. Classics like Dungeon Master, The Bard’s Tale, and the D&D games (Eye of the Beholder, etc.) I consider good. High playability is a very important factor to me, and I simply do not consider FF playable at all. Most of the time is taken up looking at cheesy cartoon characters having half-baked cute conversations. As for developing a character, it does happen, but according to the lines, plots, and stages that the game developers lay down. In Dungeon Master, on the other hand, you had much more flexibility, although of course no cute half-baked conversations.
For a modern example, take Diablo. It is practically the same concept as Dungeon Master, just a different point of view and more technically advanced. And of course you can play it over the Internet with other players. That’s where the future lies. Adapting Final Fantasy for play over the Internet, however, will be rather useless unless the game developers get a clue about playability and player intelligence (playing Final Fantasy always gives me the feeling the developers think I am stupid).
As this post shows, it is more complicated than just a few categories.
How about this expansion?
All games are turn based or real time.
With a turn based game, the computer waits for you. You can surf the net (SDMB for preference 
) while playing.
RPG - as above. Baldur’s Gate 1 is a real time RPG. Pool of Radiance (I’m going back a bit here!) was a turn based RPG.
Adventure games are similar, but may involve solving puzzles to progress, rather than character development.
FPS - as above. The games where your viewpoint is your weapon (bit crude, but I’m sure you understand) are usually real time. Thief or Quake come to mind.
Now it gets tricky. Eye of the Beholder was a real time FPS. But it was based around Dungeons and Dragons, so had RPG elements.
RTS - I would prefer to call this category God games, since you oversee everything.
Age of Empires involves real time production of military units and organising the economic resources to build them.
Civilisation 1 + 2 involves the turn based production of military units and organising the economic resources to build them, although you can win the game without fighting.
Heroes of Might and Magic 3 is turn based. Some would call it a war game, but it is similar to Civilisation, except the emphasis is more on troops (than economics).
Sim City is a turn based simulation. You try to keep economic control. Sim Ant involves keeping your colony alive.
War games usually qualify as turn based control of armies (rather than characters), and probably simulations as well. (American Civil War or WW2 are frequent scenarios).
Sports games are usually real time simulations for team games (football) and turn based FPS simulations (golf).
Hope this helps (and makes sense - I was playing Heroes until 05.12 this morning.) 
OK, I understand your point of view, but we should be clear that when talking about computer games in general, Final Fantasy and it’s ilk would always be classified RPG, without qualification.
I’m afraid you really aren’t getting the gist of this. Saying these differences are “cosmetic” is like the casual observer saying basketball and soccer are basically the same, just that in basketball the goal is smaller and everybody can touch the ball with their hands. But closer examination reveals that the rules and gameplay are significantly different. And if you say Quake is just cosmetically different from Rollercoaster Tycoon, it’s like saying NASCAR is just cosmetically different from ping pong.
If you were to actually play Starcraft (a RTS), Battlezone (RTS/FPS), Quake (a FPS), Thief (semi-FPS), Fallout (RPG), Panzer General (wargame), and Grim Fandango (adventure), you would see that these games are all quite different in terms of gameplay, not just appearance.
To clarify some of the other types of games:
An adventure game is actually one of the oldest types of computer game, pre-dating RTS and FPS. Basically it involves exploring the game environment, picking up objects, and using them to figure out puzzles that advance the story. Most RPG’s incorporate the story-telling aspect of adventures along with the role playing elements, and there is some blurring of the line between what is RPG and what is adventure. The pure adventure game, however, does not usually have hit-points or character attributes that you acquire.
The first adventure games were text-only, and first widely distributed one was aptly named “Adventure”. Infocom popularized the text-adventure genre with the Zork trilogy, Planetfall, Hitchhiker’s Guide to the Galaxy, among many others. Eventually, as graphics became better able to represent objects in a realistic fashion, the text adventure began to die off in favor of the graphical adventure game. First games used both text and pictures, and eventually the typing was phased out in favor of point and click. No longer did you of type “walk east” to have the computer describe your environment as “You are in a maze of twisty passages, all alike.” Instead, you’d usually move your character around the screen with the keyboard, mouse, or joystick. Sometimes action or combat elements are thrown in to these games, but most of the time they revolve around solving puzzles within the story.
The wargame predates the RTS as well, unless you consider actual war an RTS game. They extend from real-life military wargames that armies use to test strategy. The computer wargame evolved from games like Risk and Axis and Allies, only with much more realistic rules and conditions. The idea is to really play the General, either in a reenactment of a historical battle, or hypothetical ‘what if’ scenarios. Turn-based games in this genre can actually still be quite realistic, as generals throughout history did not usually get real-time feedback because they often could not see the whole battlefield and it took time to relay orders to the troops. (A turn-based version of Quake would be very strange indeed, although if you ever try to play a game over a 28.8 modem, that might be what you get.)
Before the grognards jump on me for that one, let me emphasize the word “like”. I only mention Risk because it is one of the few wargames most people are familiar with.
Glee: Sim-City has always been real-time, AFAIK.
mrblue92,
you’re probably right. I haven’t played Sim City, but a pupil told me it was turn based.
So no doubt it’s more like Railroad Tycoon. It’s real time, but you pause it to change strategy.
MC,
I see what you mean about viewpoints and entities.
I much prefer turn based games, so I make that a needed definition of a game.
I agree with your definitions, except this one. How can “turn-based” game also be “Real Time”?
Close, but not quite.
RPG’s can be basically single entity games (Fallout, Quest for Glory) or switchable (I can’t think of actual ones off the top of my head, but it’s technically possible).
FPS’s can be switchable - Rainbow Six.
There are text-based games with zero “entities”, like Balance of the Planet. Or multiple entities you can control, but mostly indirectly, like Rollercoaster Tycoon and SimCity.
In any event, the part I took issue with is the “cosmetic” label. The logic that drives a FPS vs. RTS games vs. RPG’s is extremely different in each case. Even if you were to closely examine two FPS’s, you could would find significant differences–say Rainbox Six and Half-Life. Sure, they may share some of the same code in certain areas, but the differences are much greater than just cosmetic. Games that in appearance are very similar can be extremely different in actual execution–sometimes that’s the only difference between a dud and a masterpiece.
Corvette or Chevette? What’s the difference? Just cosmetic if you never drive either.
Uh… I meant “could”. There are quite a few FPS’s that are based on the exact same “engine” and are mostly cosmetically different. One could argue that within a some specific genres, the majority of the differences between games ARE only cosmetic. But that’s not what you said…
MC, why are you trying to classify games this way? You seem to have a goal, but it’s not clear. It would be easier to enter this discussion if we knew why you have this need to claim that most games are similar in these very broad ways.
So far, it seems that you’ve gotten a couple of ways to broadly categorize games: by whether you see the opponents pieces, amount of chance involved, and the control of game elements. You could come up with many other fairly arbitrary bins in which to throw the various games [such as: computer opponent vs. human opponent, collaborative vs. competitive, color of the box it comes in, etc.], but I wonder if any of it is helping you. Again, why are you interested in forming this taxonomy?
Except nobody in the game industry classifies games that way.
First some background. I am a professional computer game designer. I was the lead designer on the first person shooter Rainbow Six, which is mentioned elsewhere in this topic. I have worked on both action and strategy titles on both PC and console.
RTS, FPS and RPG are rough genre classifications. They’re a shorthand used to lump together games with similar gameplay (and therefore overlapping customer bases). They’re not meant to be a precise partition.
GamesBusiness weekly breaks the major genres down this way:
Action
Adventure/RPG
Puzzle/Misc
Strategy
Simulation
Sports
Racing
Action games include first person shooters, but also platform games like Tomb Raider and fighting games like Tekken. They’re designed for people who like (mostly) mindless action, without much story or problem solving.
Adventure/RPG games are focused on atmosphere and narrative. They may have action or puzzle elements, but they’re primarily targeted at people who want to be told a story.
Puzzle games are abstract exercises in mental gymnastics. Tetris is a classic puzzle game.
Strategy games are about problem solving too. They differ from puzzle games in that in a strategy game you’re playing against a computer opponent, while in a puzzle game you’re playing against the rules. It’s like the difference between gin and solitaire. Strategy games can be either turn-based or real-time.
Simulations are Action or Strategy games that try to accurately model part of the real world.
Sports games are Action games based around real world sports.
Racing games are Action games based on racing real or imaginary vehicles.
Note that some of these designations seem to be completely arbitrary: Why aren’t Racing games part of the Action genre? When does something cease to be a Strategy game and become a Simulation? The reason these divisions exist is because they’re useful target markets. A guy who buys a ultrarealistic F-14 flight simulation is more likely to buy an M-1 tank simulation the next time he goes to the store than he is to buy a cartoony flying game. A girl who likes football games is more likely to buy a snowboarding game than a wargame, even though picking football plays and picking battlefield manuevers are very similar play mechanics. Classifying games by genre helps developers and publishers focus their effort on their core fan bases.
The current popular genres more consistent than you think, although there are fuzzy areas in between them. Trivial pursuit is the same group of games, of course its various offshoots are going to play in the same way. Try comparing trivial pursuit to chess, and then tell me if there is any similarity in the game play (apart from the fact that they are both turn-based). Of course not.
Electronic games are classified primarily according to their play AND their appearance. These are two elements that are important: as was noted, basketball and football are not the same sport.
Your best bet now is to go play an RTS and an RPG and notice the differences yourself. You will find the same differences outlined in this thread during your first 15 minutes of play.
By in large computer games are classified by gameplay as well. Playing an RTS and playing an RPG are very different experiences.
Here are the key gameplay difference:
RPGs are focused on winning battles to make your character (or characters) more powerful. Most RPGs have no notion of resource gathering or base building.
RTSs are focused on collecting resources and building bases to make your army more powerful. Most RTSs have no notion of character progression.
This fundamental difference in focus has a profound effect on gameplay. For example, fighting lots of little battles is a Good Thing in an RPG – that’s how you build up your characters and ultimately win the game. Fighting lots of little battles in an RTS is Bad Thing – instead you want to establish a defensive perimeter and focus on exploiting your available resources so you can grab larger and larger parts of the map by crushing the enemy with overwhelming force.
At the core the two genres are very different – they only resemble each other superficially in that you’re controlling units by clicking on them and issuing orders. But that’s like saying that Trivial Pursuit and Monopoly are the same game because they both involve rolling dice and moving pieces around a board.
But these are all versions of the same game. There are parallels in the computer game world. For example you can buy Rainbow Six (the original game), Rogue Spear (the sequel), or any of three mission packs (Eagle Watch, Urban Ops or Covert Ops). They all play the same way – they just have different storylines and mission settings.