What is your opinion about Heroes IV?

I don't think it's fair to call it an unsuccessful experiment. It's more like a revolutionary idea, and whether it's good or bad is a matter of personal opinion. Overall, the variety has increased compared to other parts, but not always for the better. Personally, for me: (positive innovations) + hero on the battlefield + magic and skills are divided (by schools) + choice of development path in the castle + other innovations (failures) - army moves without a hero - a lot of potions and elixirs (could be fewer) - reduced number of castles - few monster buildings (out of eight, you can choose three, and two are mandatory) - no unit upgrades - small income