It's not cartoonish at all; it just has brighter colors than in the third game, and sometimes they can be irritating – I won't argue with that. But it's definitely not cartoonish.
It wouldn't hurt to improve the graphics to make them more serious. It's not cartoonish; the engine was just made poorly, and it looks too much like the Warcraft engine. They should have made the graphics like in Disciples 3; that would be serious graphics and definitely not cartoonish...
