I actually liked Heroes 4; at first, it was a bit unusual, but I eventually got used to it. However, I tend to think:
1) The player should adapt the game to their preferences, not the other way around!
2) The game should be enjoyable and engaging (which Heroes 3 did brilliantly!), not something that makes you think, "Just one more level, and maybe it will get better..."
3) Everything should suit you!
Based on this, Heroes 4 was a failure (in my opinion), while Heroes 3 was much better (even if the graphics are outdated) in all three aspects.