The main campaign is absolutely amazing at first and it's long as fuck. It goes downhill after the dwarves vs undead part until you hit pic related (2/3rds into the main campaign). Then it is just straight fucking aids. You have to hastily build up an army with one of the must resource wasteful races in a desert with only enough resources to do 1 push, and then basically plow through a straight line that sends waves of demons 2x your units levels using AOE fire spells (that progressively get stronger), with 3 MASSIVE AOE rain of fire spells that span the entire width of the pit, a bulky as volcano golem who tanks hard as fuck, and then a huge pit of enemies at the end. AND YOU NEED YOUR ARMY because theres a fucking boss fight. The game changes completely. Instead of holding off waves of enemies until you could get a superior army, you basically have to rush out your army as fast as you possibly can and get it to the end with any means necessary it's not fun. I could only beat it by cheesing hard.
From there on the game continues this trend of just putting you in situations where resources are scarce as fuck, or the units massively out level you. I remember a swamp full of waretigers that would oneshot your units, that would come in groups of +5. It doesn't get good again until the very VERY last level.
The first expansion is pretty shit/mediocre. It starts out really fucking bad. You're tied down to 2 invincible NPC units who follow you around to do the fighting for you. They draw aggro a ton and if their health gets low enough they limp back to you, so the mobs will just rape you. The RTS parts don't get in until pretty deep in, and when they do, they remove fucking towers for the first half or more of the game. Even when it's back to business as usual it's nowhere near as fun as the main campaign. Also you have to grind hard in this one. I never really grinded in the main campaign, but for the first expansion I had to leave my game on overnight just to keep my character leveled enough so he could use the next level units.
The last expansion. Idk. They changed the voice actor and it felt like more of the same shit. The second expansion put a bad taste in my mouth so I just quit. Honestly, I'd just play it for the main campaign then quit as soon as you hit pic related. The game basically dies there.