the combat primarily. there were lots of complaints relating to the progression and exploration, but those seemed like they may have been concerns that were exaggerated because those parts of the game had changed significantly from when it was in alpha.
what i didn't expect was that the combat is completely and unconditionally horrible to the point of being borderline unplayable. everything has crazy amounts of health and kills you in a few hits without having any real indication of what their range is or when they're attacking.
this is exaggerated by the fact that it's an open world game with roaming packs of monsters. that wouldn't be so bad if it wasn't for the fact that as far as i could tell enemies only have 5 levels that are equally present in every part of an area despite being insanely different power levels, so when you start out you literally don't do damage to anything other than level 1s and 2s with the 2s still being practically unkillable but you'll be seeing as many 3s, 4s, and 5s.