I just bought the game a couple days back and am fully patched up and playing on a modern system.
Overall, I am very happy with the game play, but I am still getting a bunch of crashes to desktop and the like, and these are not wholly unexpected with a just released game. On windows 7, I do seem to get a game crash each time I tab out to windows, so I don't do that...
I also frequently lose the combat sounds during a battle, and they stay "lost". Happens at different intervals, but it almost always happens. And the spell/combat effect graphics are a bit touchy too, the graphic for the second spell of a combat round firing from off the screen and the like.
I have also been running into some creatures with bugged stats, especially later in the game. Of note, I got a Pack Drake roll into one of my towns that had 38.4 million health, and the game really thought it should have that much health, it hit one of my combat heroes for 14 million damage. Where does a drake with 38 mil health go? Anywhere it wants.....
I am sure a lot of that stuff will get picked up during the patching process, but I thought I'd put this stuff out there, if other people are seeing the same things.