[Edi]

HoMM4 became a good game once they got both expansions out and patched it to version 3.0, but at release it was an unplayable piece of crap that tried and failed spectacularly to steal a lot of features from Age of Wonders 1. Get the H3 & H4 Complete DVD. The experience with the new HoMM4 is light years removed from the first release crapware. I can vouch for that from experience.

HoMM5 has the biggest problem with the AI being slow and the graphics engine being slow. The AI is probably because the damn thing sees the entire map and evaluates everything on it before making moves, whether it can reach stuff or not. Load up an impossible sized Tribes of the East map and you can't play them with AI on, because turn resolution takes 20+ minutes.

The skill system in HoMM5 is pretty revolutionary compared to the old ones in the series, with much more choices. The problem with the original release was that you only had certain limited must-have choices and you only had one or two viable heroes for most factions. Tribes of the East revamped the skill system and enriched it a lot.

H5 does still have the same old killer stack and critical mass problems of earlier Heroes games, but they're not necessarily as bad anymore. A well designed hero, especially with the right spells if a caster, can wreak absolute havoc on even a large enemy army. I've gotten wiped out several times against the AI that way when I had the edge numerically and ran into something that had just the right things stacked on it.