S.T.A.L.K.E.R. 2: Heart of Chornobyl was reviewed rather well at launch, but fans and critics noted that the game was awash with bugs, something that developer GSC Game World has since been trying to fix.
The first patch of this year brought 1700 fixes and improvements to the game, and Patch 1.3 manages a whopping 1200+ changes. AI will now be more responsive, with enemies detecting your footsteps more easily, and mutants move more smoothly during combat. Also, with some nerfs to some artifacts, you might find combat a bit trickier.
But, there are buffs elsewhere to keep you alive while roaming around the Zone, as well as new death screens, extra audio and animations that just make the game overall feel more complete, including new VFX animals and a new type of anomaly. Check out the lengthy patch notes here.