I started playing as the mages and quickly realized that it wasn't interesting for me. The difficulty doesn't seem to have any effect at all (although I chose Heroic). It's, of course, silly to judge based on the first mission, but I feel like I'll have to force myself to play to get further.
Basically, I'm only waiting for interesting games with real opponents in Heroes 7. Today I'll try single-player maps with AI, let's see how it goes...