It's just all the stuff that actually has to do with player characters I hate. >.< Powers bad. Tieflings and dragonborn as core races worse. Everybody being basically the same combat-oriented class with a different skin worst of all.
Plus, that they threw away Greyhawk, and trashed Forgotten Realms yet again.
And the "dungeon delve" format. But that at least I could avoid that by playing Goodman Games modules instead if I wanted to.