Well, the game is one of the buggiest games I've played in a very long time. Gameplay is really good, but it does not work properly for me.
Bugs I've encountered thus far (played through the short Haven campaign (4 maps) and a single skirmish level (small, 3 opponents)):
The game does not close properly. When I exit it, there is still a process running in the background, and I need to enter the task manager to close it.
The special skill that marksmen has does not align properly, and sometimes "starts" from the wrong place.
I had issues with the game not accepting me assigning skills, and during the 4th level on the haven campaign, I could not pick any of the "inner" skills.
Pillaged resources (like mines and lumbermills) stay pillaged forever.
XP-bars don't work properly when you crush an opposing hero (seem to be some rollover problem)
Some names are placeholders (like the poetically named mName)
Many graphical effects don't align properly. It does not impact gameplay, but it gives a very sloppy impression.
Killed heroes still show up on the minimap for a few turns
Heroes sometimes get some of their movement points back when entering a town screen.
Heroes sometimes don't expend their entire move when moving, even though they got order to do so.
When entering the town screen for a recently conquered town, a dead enemy hero was showing as present in the town (the hero that guarded the town when I conquered it). I could set the hero as "leader" of that town, despite it being both dead and not mine.
Random stack of Plague Lamasu appeared on my side during combat (I got 10 of them for some reason)
The game does not always show the correct damage you'll deal when mousing over an enemy during combat. This seem to be because the damage shown does not take into account certain defensive properties (it takes some into account, but not all).
Sometimes the game won't show the expected damage at all when mousing over an enemy.
The location of treasures are not always correctly shown when you've visited all obelisks.
The AI is daft. Alright, so that might not be a bug, but it keeps sending level 1 heroes with either no or only a handful of creatures into my territory. Those will just move right past my high level heroes with big creature stacks.
The vampire special ability that should let them revive parts of their stack upon attacking the enemy does flat out not work.
Would I recommend the game? No, not in its current form. I've played 5 levels and discovered that many bugs, without actively looking for them, and to me that indicates that it was not ready for release.
Oh if you can wait, definitely wait. There are plenty of the typical release bugs that'll probably get fixed in the first week. Personally I haven't found any campaign stopping bugs yet, but little bugs sure.
There are known campaign stopping bugs on haven level 2, 3 & 4, necropolis 2 & 4, stronghold 3 & academy 2. Actually, the ones on Haven 2 & 3 seem to be very common and easy to trigger (Haven 3 actually has 2 known showstoppers).
I'm fairly certain that the only version of HoMM in which the AI could put up any fight in a balanced multiplayer game was HoMM 1. In all of the others it was generally a pushover to varying degrees, although some were better then others. The HoMM 1 AI was quite challenging though, probably because the game was much simpler and there were many fewer decisions for it to make.
Campaigns are another matter entirely though, and most versions of HoMM had campaign maps that were quite challenging on hard.
The AI in the first 2 HoMM games cheated horribly. They did not change much between the difficulty levels, apart from how much the AI would cheat.
