I had never played the fourth one beyond "knight" level; I loved it for its plot and "freshness." I hadn't played them in about five years, but I encountered no problems with the map, even though I feared I wouldn't be able to handle it.
I wasn't familiar with the literary source material, but after the first day of the Walkthrough, I already started reading it. %)
I would never have even imagined that a quiz, a chess study, battleship, "blackjack," and other things—which I won't list so as not to spoil the surprise for the player—could be implemented on the Heroes IV engine. And all of this is accompanied by magnificent text, music, and a wonderful sense of exploration and novelty.
Seriously, the word "recommend" doesn't sufficiently describe my opinion here; it is truly a must play if you can stomach "the fourth one" even slightly.