Absolutely nothing. Pretty much everything that people complain about (No Ice Climbers/Lucas/Wolf/Mewtwo/KKRool/Ridley/etc and too many clones) don't really faze me. For starters, while Ridley would've been cool, and it's odd that IC got cut after being in two games, I got everything I wanted and more (Bowser buff, Robin, and then more with Palutena, great new stages representing Earthbound, Fire Emblem, Kid Icarus and Paper Mario, Smash Run is cool, less laggy online play and a random online mode that isn't all "item lag insanity" that lets me actually fight with a random 1v1.)
Like...I can understand the cut of Ice Climbers distressing some, and possibly those other modes if you really liked those (I always found them a fun distraction at best, but hey, I get that people like them.) but aside from that I don't see anything to complain about aside from rediculous clone arguments (SSB4 has 6 clones, Melee had 5 clones with half the roster of SSB4) and obscure/fan-favored picks. In regards to that second part though, to be fair, we're not dealing with an ordinary man. He doesn't exactly cater to the fans' every whim.