What is your opinion about Heroes IV?

R.3.M.
I've played through all the games in the series. I strongly suggest you "play through" the fourth one.

P.S. Just listen to it: Three, Three-y!!! And then here is Four, the Fourth part.... Fie!!!

Ossified fanaticism or, otherwise, a matter of taste.
Four isn't "fie." You just need to play without muttering under your breath every three minutes: "Three-y... three-y... three-y is the best..."

Added after 3 minutes
R.3.M.
There's also this point: when you really like something, you move to the new one with great reluctance; it's always hard and always unpleasant to play at first. I started with two and four, and I got used to three, although at first many things drove me crazy.
You need to play it, preferably forgetting for a moment about your "beloved three-y" — then, I am sure, a multitude of interesting moments will reveal themselves.