They went a few steps further then just a graphics update - although that looks amazing too. They actually redid the AI so their no longer derpy, they actually flank you in groups much like the 2nd game, the ai is just smarter in general. Theres lots of quality of life updates to movements and scrounging and whatnot, they cleaned up alot of the cutscenes as well which look amazing. overall story is naturally the same and untouched, even the amount of mobs/ai's are supposedly untouched. Very much the same game just way more polished if you ever have plans to play it again Id recommend.