Me too!
That’s easy to say now, 25 years later, where FPS is an established gaming genre like RPG or fighting games. Was it widely considered easy in 1993/94 by the average gamer, when it was basically the first game of its kind? (I’m aware its not the first FPS, but ancestors such as Wolfenstein 3d had nowhere near the same degree of popularity.) I’m not so sure that it was.
New user created maps are still uploaded to doomworld.com on a regular basis.
A number of ports are available (such as GZDoom) that can play Doom on modern machines, including those running Windows 10.
There are unbeatable games.
Some of them are old arcade games where there is no final win condition, you just play until you lose or the game crashes. Pac-Man is famous for having a kill screen, which is what the game shows when it crashes, at level 256. You can play Pac-Man up to level 255, but at 256, no matter how good you are, you can no longer continue to play the game.
Other games are unwinnable because of bugs. Mission: Impossible for the Commodore 64 is an example, but there are tons of others. Again, you lose (or do not win) because of a software fault, not any fault of your own.
Other games can become unwinnable because of a decision you made at some point which doesn’t end the game immediately, such that you can be playing an unwinnable game for an arbitrarily long period of time. Old text adventures and some graphical adventures are notorious for this.
And some games are effectively unwinnable unless you memorize exact level layouts, because the enemies and terrain come at you so fast there’s no way to react quickly enough unless you know it’s coming. Battletoads for the NES is absolutely notorious for this, to the point it’s the main reason the game is remembered at all today.
That said, the original Dooms for the PC don’t fit into any of those categories. It is absolutely possible to beat Doom and Doom II without cheats.
I’m not a particularly good gamer, and I was able to beat Doom and Doom II (and Hexen) without cheats. It took me a lot of tries, but it was certainly possible.
But just for the sake of completeness, there were two different codes for invulnerability: iddqd and idspispopd (the latter is an acronym for “smashing pumpkins into small piles of putrid debris”). idkfa was the code for full ammo and all keys; for just full ammo it was idfa .
Centipede worked similarly. On each level, a segment detached and became a head, so on level 1, you had a 12-segment 'pede, on level 2, you had a loose head and an 11-segment 'pede, and so on to level 12 where you just had 12 discrete heads. But when you beat level 12, it would start sending the 'pede segments onto the screen, but then realize that it was trying to divide a 12-segment centipede into 13 segments, and crash. Though of course, you could say that on a game like that, reaching the crash-point is beating the game.
Yeah, throwing my weight behind the “Sure, there were unbeatable games, but Doom sure wasn’t one of them.” crowd. I certainly beat Doom back in college. It doesn’t even come to mind when you say “Hard game”.
Actually, I think by the time Doom came around, really stupid hard stuff was on the way out – most of the truly hard hard stuff was late 80s era. That was when you had your Castlevania, your Ghosts’n’Goblins, your Sylpheed, your Sinistar and, indeed, your Hitchhiker’s Guide to the Galaxy text adventure (one of those “becomes unwinnable if you do something ‘wrong’ early” text adventures mentioned) and the like. Doom didn’t come out until 1993, which was moving onwards into the Super Nintendo era, of, honestly, more playable, better games. 
I also agree that if you’ve got a game that crashes before you “beat” it (basically, because the designers never thought anyone would get that far – it’s not like they were coding elaborate ending cinematics in Pacman and Centipede) then you HAVE beat the game.
IDSPISPOPD wasn’t invulnerability, it turned clipping on and off, so you could walk through walls. In Doom II, it was supplanted by IDCLIP.
You could get the temporary invulnerability powerup on-demand with IDBEHOLD and then V.
I remember Doom. The hardest difficulty in the original (the respawning monsters came later) was reasonably easy to beat: the trick was to get the demons to fight each other. The final level of Doom 2 was a bit of a lottery in that you had to fire your rockets at just the right time.
Oh yes, in the original, using the chaingun in deathmatch could crash the network.
I beat Castlevania and Ghosts’n’Goblins on my old NES back in the day, both without cheats. They both required lots of playthroughs and practice to memorize what enemies will show up where and when, and how to kill and/or avoid them. It helped that I was a little kid that had the luxury of sitting in front of a console for hours. Can’t do that these days with a family and other obligations. Luckily most games now let you pick up exactly where you left off without losing progress. That’s what made many of those games a challenge… They were marathons that you’d have to start over again if you failed too many times.
Ah Doom. I learned more about computers and networking playing Doom than I did in college. Also spent more time playing it than studying.
I think it was a regular Doom II wad. You start the level on a rectangular island full of monsters. I’d run into a room, fire a few rounds at the pursuing monsters, and stay in there until they killed each other.
Thanks for all the info - lots of memories brought back.
I don’t recall which version we were playing, but it seems to me we finished the basic level. The game had options to go to harder versions and it was there we hit the problems. Maybe that’s what I was referring to in my OP.
The demons etc, would respawn as soon as they died, as fast as you could kill them with rockets and chainguns. (I loved the chaingun!).
We weren’t playing on a network, only a bunch of guys on individual PCs playing solo.
If there were respawning monsters then you were playing on Nightmare, the hardest mode. It not only had respawning enabled but the monsters as well as their fireballs also moved faster. There were also more of them and they were a lot tougher to kill. Nightmare mode also disabled the cheat codes, so if you couldn’t finish the game without cheats then you weren’t playing on that.
Count me amongst the Doom was not impossible to beat without using cheat codes crowd. I beat it on the second hardest level without cheating. (The hardest level really doesn’t count since you don’t really “beat” the game if you consider 100% of kills and secrets being found, since enemies respawn.)
I also never went for “par” which was a time determined by what it would take for someone who memorized a level to get through it without trying for the secrets. I will say, I did look up where some of the secrets were, because some were rather difficult to find. Particularly the ones where a secret door would open up when you stepped on a certain area and you had limited time to find the thing before it closed.
Also, in one of the episodes (I think it was 2, might have been 3) you could only get to the secret level of the episode by standing in a certain ledge, facing the wall, and firing a rocket launcher at it, thereby taking a lot of damage but blowing yourself off the elevated ledge and into the opening where the door to the secret level existed. And, you couldn’t do it on the easiest difficulty setting since the concussive force of the rocket launcher when blowing oneself up with it wasn’t strong enough to kick you backwards far enough.
And as mentioned, IDSPISPOPD was the no clip cheat, not a god mode cheat.
But Doom was a completely fair game even on the hardest level that didn’t have the respawning enemies.
Although Episoide IV had the one level where you could trigger somehing like nine Barons of Hell that are standing behind a square divider that has a Nine-Inch-Nails logo on the floor (the guys from ID were huge fans of Trent Reznor so much that they had him do the music for Quaike, IIRC). I died many times trying to kill them all without dying. Fuck that level!
I think I remember that. There was also a Cyberdemon and an invulnerability powerup. The trick was to get the powerup and get the Barons to fight the Cyberdemon.
Add me to the list of non-elite gamers who could beat Doom. As I recall, once you mastered circle strafing, it wasn’t too hard.
The really good guys could beat it with style. There are probably still youtube videos of guys going through levels in just a few seconds, or getting 100% kills and all secrets, or beating the game in “Tyson mode,” which meant 100% kills with no advanced weapons, just fists, chainsaw, and pistol, or pacifist mode, which meant not killing any monsters but getting through all the levels.
I thoroughly recommend people try the Brutal Doom mod. Turns the gore up to eleven.
I always had trouble with Doom because the playing style necessary to beat it conflicted with my game instincts. Doom required you to take maximum advantage of enemy fratricide and the way to do that was to throw yourself into the meat grinder and run and dodge like crazy. I’m terrible at that, so my instinctive style is stealth and ambush, taking out enemies one by one and never fighting melee if I can help it.
Sorry, I didn’t mean to imply that any of the games I listed were unbeatable, merely that they were a lot harder than Doom. 
I don’t remember melee ever being a good idea in Doom except maybe to save ammo by chainsawing the ineffective melee “demons”
Have the original game makers commented on Brutal Doom? I bet they see it and think it is more like what they wanted.
Can you look around 360 degrees in Brutal Doom? I know the camera was fixed in the original games.
I believe they have (someone will be along with a link shortly), saying that is more like what they wanted but the level of ultraviolence was considered unpublishable at the time. Elements, such as the finishing fatalities, did get incorporated into Doom 4.