That was my experience, too – the main campaign was roughly my preferred difficulty level (although a few of the scenarios took multiple tries) but some of the optional campaigns I tried were too frustrating and I gave up on it. In my case, I just didn’t like some of the army lists either (dragon guys, I’m looking at you).
I blazed through my first few scenarios of *The South Guard * on easy thinking I’d figured it all out and should play my next campaign on a higher setting only to be smacked around by the undead in an underground scenario. All of a sudden my archer-heavy army wasn’t doing much damage at all, a good lesson in the importance of the damage type mechanic.
I’ll certainly be taking my time before tackling the Expert campaigns.
By the way, this comment made me think…
When I was playing it, my favourite traits were (in order):
Strong
Quick
Loyal
everything else
Having an army full of Quick units was a big advantage, I thought – much more advantageous than the few extra hit points that Resilient provided, for instance. Anyone else feel the same?
Really? STRONG as the best trait? Honestly, I think strong is competely worthless on a lot of units and of only marginal benefit on others - it’s pretty much irrelevant on an archer or any sort of magical unit, and it’s fairly trivial on units with low numbers of attacks as well. It’s obviously very nice on the Elvish Fighter, but it’s kinda lame on say, Heavy Infantry. Definitely a trait that I want on some units and not others.
Quick is nice, but the HP loss hurts a lot on frontline units (Especially since it takes up a slot that could be a hitpoint INCREASING trait), and a lot of the time your army is governed by its slowest units anyway. I will pretty much always take a Strong/Resilient fighter over a Strong/Quick fighter. It is very nice on ‘scout’ type units though.
Loyal, IMHO, is hand’s down the best trait in the campaign. Resilient is the only trait I welcome on ANY unit. Intelligent, overall, is the least good, but it can be really useful early on to get a few units up into later levels quickly.
Obviously I didn’t mean that Strong was the best trait on units that don’t benefit from being Strong. I’m not that dumb. 
In most games, I’m a believer in the idea that “the best defense is a good offense”*. Obviously you can’t be too disappointed by the Strong trait since you were the one suggesting Strong/Resilient fighters!
- -Mel, the cook on Alice
Of course I was. When the choices for what to put next to Resilient are:
Quick, which I was arguing against
Intelligent, which is of…selective value at best.
and Strong
I think the choice is fairly obvious.
Given the choice, I would prefer Loyal/Resilient, but Loyal doesn’t usually come with other traits, and it’s not a “random trait”. But Loyal is the #1 best trait for ANY unit.
If you want to start factoring in racial traits, I’d probably rather have Resilient/Healthy, but that’s pretty specific.
The best defense may be a good offense, but you’re going to be defending sooner or later, and trying to kill all the badguys before they can concentrate fire generally doesn’t happen.
Edit: the best thing about resilient is that you can always count on it. You ALWAYS have 5 (or more) hps more than you would without it. Strength only matters if you are fighting melee AND hit.
Psh. That means reslient is only worth anything when you get below 6hp. Any HP above 1 is extra.
That’s my take on it as well: it’s only useful (albeit extremely useful!) in that small window where your unit has between 1 and 5 hit points, which doesn’t happen very frequently in the course of a game, whereas you’re attacking or moving just about every turn.
I disagree; It’s relevant anytime you have to make a “Do I have enough hitpoints to take this action” decision. That’s anytime you attack, and anytime you move to or stay in a spot in which you might be attacked. Which is to say, CONSTANTLY.
“Do I attack that orc? Well, he can’t kill me even if he hits all three times.”
“Do I fall back to a village? No, because he doesn’t have enough units he can bring to bear to kill me.”
These are essentially the sort of logical decisions you need to make everytime you do anything with a unit, and resilient improves the odds of you being able to make a “good” choice. It’s not about whether your unit is or is not dead. It’s about whether the decision you are about to make could kill him or not.
So I played through South Guard, and am considering starting heir to the throne. It’s a fun game, but too much of a time sink in the way I’m playing. i.e every time I lose a unit, particularly a leveled unit, I go back a turn or two and try and replay. Not only is this starting to feel like cheating now that I’m not completely new to the game, it’s also getting tiresome. What keeps me doing it is the “I will need these guys in the next levels” sort of mentality. Is there a rule of thumb for how many leveled fighters you should be taking into or out of scenarios? For e.g. - “By the time you clear scenario 1, have 2 people leveled up. Going into scenario 5, it would be good to have at least 4 level 2 and 1 level 3 unit.” I’d much rather not find this stuff out by trial and error.
Losing a unit you’ve carefully nurtured through several scenarios is annoying. Especially when it feels like you’ve been screwed over by the RNG (‘How the hell did those two skeletons hit me all three times with only a 30% chance to hit?’). There are walkthroughs and the like on the Wesnoth wiki, but I’ve avoided them.
I’ve only resorted to savescumming a couple of times, but then I do play on easy…
Oh and Loyalty all the way on the favourite traits thing. No upkeep rocks.
It annoys me too. What makes it worse is I don’t like the cannon fodder strategies because I tend to keep only the new ‘loyal’ troops I get, and hang on to all the other troops I recruited in the first couple of scenarios. I’ve been savescumming a bit now. Usually…usually…this is not to game the RNG but try out different tactics which don’t get my guys killed.
ETA: I’m playing on normal difficulty, so death can and does happen regularly.
The GAME MANUAL actually comes out and says:
“Losing units is expected, even advanced units.”
and
“Don’t sweat it too much when you lose some units. The campaign was designed to accommodate the player losing some units along the way.”
and
“After slaughtering scenarios (where you take lots of punishment) there are usually “breathing room” scenarios where you can rather easily gain some gold and experience (advanced units)”
So yeah. Relax a little. 
While most of those statements (particularly the last one) were probably written with Heir to the Throne (aka “the original campaign”) in mind, they are also emblematic of the design philosophy of the team.
In the end save scumming is a lot more tedious that simply starting over once you realize you don’t have a strong enough army to continue. You get better at the game without doing it too.
I’ve been thinking a lot about this game lately and i remembered how to beat siege of elensfear: send the thieves into the fort and take over some towns there, it will make the main force pull back to deal with them and let you get out of the moat into the fort proper. Then deal with them before the other force comes down. It will cost you some of the loyal thieves though.
I always consider it a win if I come out of that mission with more than one thief surviving. 
bldysabba - I tried to get through A Tale of Two Brothers on challenging and just got smashed up by waves of Elvish scouts in the second scenario. The total absence of healers makes it challenging - especially when skirmishers bypass your main body to smash up your dented guys getting R&R in a village. It was Dwarf Fortress type fun. So back to the start and a notch down in difficulty for me.
I want to finish An Orcish Incursion as well before I tackle Heir to the Throne. I’ve had a go at it, but by scenario 4 or 5 my recall list was pretty stuffed (aside from a couple of Druids and a marksman ot two). I am getting better slowly though, I’ve learned the true power of a slow attack for instance.
Airk and DigitalC - yes I saw that in the manual and try to play that way on the whole. I’m guessing ‘Siege of Elensfair’ is a scenario in Heir to the Throne? Obviously one to look forward to.
On my 4th time on The Alliance in the Legend of Wesmere campaign, and no matter how pumped up my team, no matter the strategy, I’m still not even close to completing it.
I’m skipping the campaign and moving on (luckily there are quite a few campaigns), but I’d love to know if there are any more levels that are just killer like that? I hate spending so much time building up and still getting creamed on one level.
So, any levels I should skip? What are the toughest in the game?
That’s essentially what made me stop playing the game:
(1) start playing one of the campaigns
(2) have fun for a while
(3) hit a level that’s more frustrating than fun
(4) go on to the next campaign
(5) run out of campaigns.
I don’t think I ever played Legend of Wesmere, so I can’t speak for it.
I didn’t find ANY of the scenarios in South Guard, Tale of Two Brothers, or Heir to the Throne “more frustrating than fun” but I did eventually get annoyed with the Desert Elf campaign, though I can’t remember what it was called.