Can't enter buildings, if you play it with a controller you're screwed, hitboxes on the enemies are messed up, ghouls can shoot now, can't pick up much of anything, limited stash. It's just bad. It's really, really bad. V.A.T.S. is useless. No clear reason as to why you should upgrade anything but strength, endurance, intelligence, and luck.
It's bad. Don't do it.