What is your opinion about Heroes IV?

Not better, but different. The tactics are different, the development is the same. It's not a continuation. Otherwise, it's a pity.
Actually, it's a pity for the bee. Right?;)

Not a pity at all. Go to Heroescommunity, chat with players who have played the third, fourth, and fifth installments for several years. Any of them will tell you that "Heroes 4 is better" and "more strategic." The only decisive drawback of the fourth installment is that it takes more time to play than the other parts.