What is your opinion about Heroes IV?

Well, I don't know, I really don't. Personally, I like the 4th installment the most. First, it has fewer bugs. Second, it has Phoenixes, Mantises, and other creatures. Third, I figured it out very easily. The only drawback is that you can't upgrade units.

I don't feel the same strong love for the 5th installment as you do, but I do play it sometimes. Today, I was just playing with Draga (Life vs. Order). And regarding the bugs... you're wrong, there are plenty of them.

Added 8 minutes later

I don't like the building system in the castles, the hero skill tree, and the confusing factions. But otherwise, everything is great - the hero participates in the battle - that's cool... the premiums move on their own - even cooler... and the funniest thing is riding on zebras =)))

The hero participates in the battle - that's a bad idea. The hero will always be targeted by archers, and if the hero is a mage and you've put all your bets on him... The fact that you can move troops without a hero is also not a great idea. There are a lot of experiments in the fourth installment.
But still, if people play it and enjoy it, then it's a good game.
P.S. Tastes differ...