I've always thought that "Heroes of Might and Magic III" is much better than "Heroes of Might and Magic V". And I still think so, but the gap between them doesn't seem as big as it used to. In general, right now, only two or three things in "Heroes of Might and Magic V" bother me: the very, very long turn duration for the AI, and the fact that you can only teleport to the nearest castle and summon reinforcements only from the nearest castle. I've just learned how to play "Heroes of Might and Magic V" a little better now...
P.S. Almost forgot. The inability to find the Tear of Ascha on random maps is also a drawback.