One thing I've disliked about HoMM and, to an extent, Age of Wonders is that as a campaign advances your heroes get so powerful that they make regular troops pitiful in comparison. It gets to the point where your one guy, or one elite stack that carries over, just rampages about. You can get to a point in those campaigns where losing a built up hero might as well be a complete loss as you have to start over. Early maps tend to be lots of fun with strategy and battles between non-hero groups that matter. Later maps tend to play much differently because you've got a very small pool of uber-powerful stacks and the non-hero stacks hardly matter.
The original Warlords and Civ4's Fall from Heaven mod, being self contained games, have heroes that grow powerful, but since they don't carry over it doesn't unbalance subsequent games. Though, those don't have campaigns I suppose and I do like the continuity of story in a campaign. I like improving units, just not with significant carry-over between games.
So, I guess this is a plea to avoid designing in this kind of growing power gap between regular units and heroic units as you progress through the campaign. Perhaps hero growth that's less power oriented and more option oriented. Some examples of things that gain you strategic and/or tactical advantage, but not outright strength:
- bulk speed (able to move a stack somewhat more quickly overland)
- small uber-speed (able to fly a small stack)
- Wider range of spells or spells that given tactical advantage like throw up walls of stone to funnel attackers
- Able to lead more troops. Say, normally a non-hero stack can attack with 10 units. A leader adds +X to that, so they can bring more units to bear in a combat even if the individual units are stronger (think the tactical advantage from Mount and Blade, if you've played that).
- Morale. If you have morale loss in the game and units might flee, leader make that less likely or have a rally ability.
I'm sure there's more, but the core of each is an improvement in an army's abilities under a leader, but not a large scale increase in direct army strength. Or, if you're going to give a way to pump up an individual hero's abilities, don't give them the ability to lead a lot of troops. Make them a one-off like, oh, one of the nine minor Nazgul or something. Powerful in small engagements, but loses it's use in larger battles.
Note, I'm not against an uber powerful unit. The creation of a titan, demon, or some very powerful end-game unit. I'm against units that carry over creating an un-fun balance issue from the very start of the next game because you effectively have an end-game powered unit at the start of the game.
