The campaign feature is very very simple - but it works, is nicely customizable (though I've discovered that some things that can be customized for scenarios can't be for campaigns, while some things can only be customized by editing config files by hand), and if you just want something with a little more longevity - they might well do the trick.
There aren't really any complex systems behind it - basically, you set your force at the start, which will be worth a certain number of points, and you can select a fixed % of that amount of points to spend on either a) artillery and air support; or b) "repairing" (i.e. basically re-buying) any units you may have lost in a preceding battle. The lower the % you set, the more chance there is you won't be able to recover losses. The enemy always gets a boost based on that set %, and you can separately set a force size handicap as well.
The map selection is: you choose a campaign map, choose a battle map size (which is the size of the piece of that map each battle will cover), and can then draw a line across the campaign map, such as many points along that line as you want. When you're done, the generator splits up the map into individual battle maps. They'll generally overlap a bit with each other, and their number depends on the battle map size and length of the line you pick - could be as few as 3-5, or could be dozens. The first point you selected is basically "your base" and the last point is "enemy base".
The campaign will always start with a meeting engagement on a battle map that is exactly halfway down the line between your "base" and the enemy's (though you can change that via config editing). If you win a battle - you advance, sometimes by more than one battle map, towards the enemy's base; and the next battle will be an attack for you, with the enemy defending. Lose, and the next battle will go back, possibly to the same battle map you were on for the opening engagement. Imight be either a meeting engagement again or defense for you (depends how badly you lose the previous battle).
And it keeps going until you reach the enemy's "base" (last map in the line), or until you're pushed back to yours and have nowhere to go back to.
As far as I know, you can't customize your opponent, other than selecting a nation, general type of force (infantry, mechanized, or armor), plus things like morale/training bonuses and point handicaps. The enemy force is randomized a bit each battle. For the player force - as far as I can tell, you can't "buy" any new units (except air support/artillery, which you only get for one scenario), only restore ones you lose.
One cool feature I do like is that artillery and heavy combat will "destroy" buildings (and turn trees into leafless sticks) permanently, and in campaigns with a lot of back-and-forth, you'll notice the damage building up.
Otherwise, that's that! How is this for a description?