I strangely had very few bugs. There certainly were some, undeniably, but it was something like one every 2 hours or so. What I did notice is a staggering decline in reactivity compared to Act 1-2. I was frequently delighted by the game recognizing actions I had taken before in the early chapters, and responding to that. Where as Act 3 didn't react to my actions very much, or had much more linear solutions (Amulet of Bhaal really stands out).
In any case, remarkably coherent for a game this complex compared to recent games like the infamous Cyberpunk, Kingmaker, or Wrath. Or exceedingly buggy older games like Vampire: Bloodlines, Torment, Fallout, or the launch versions of Final Fantasy 6, Diablo 2, Everquest, or World of Warcraft. Talk about hot messes I still loved.