So, there are few drawbacks; the game is well-thought-out in every detail, except for... the stupidity of the AI... Yes, the graphics aren't great, but don't forget, this game is from 1998! It's 8 years old. Overall, I think that Heroes 6 should be made like the third one, but with added factions, units, a changed landscape, more decent quests, and a lot of other things... And there's a saying: "Everything new is a well-forgotten old."
I played the fifth one and realized that Heroes 3 is the best.