So that's a tricky one, I've been a pretty dyed in the wool D&D hater for years. I like first edition Advanced D&D best though. I've run so many hours of 5e and all I seem to do is hate it more and more. True there's that really broken Dwarf, Fighter, Barbarian in the campaign, but that's not it. So without doing a "The worst thing about D&D is that it's not GURPS or Rolemaster." The thing I like best about D&D is its wargame roots. I like the quirky, deadly, game with fast character creation, realm management, naval combat, and troop hiring rules in the core. I like the reach of a weapon determining first strike if you move into close combat. I like that combat is structured in a way that makes handling big units easy. I like the weapon verses armour table. Not that first edition couldn't be better in places, I'd integrate the weapon verses armour table with the to hit table to cut down table references. But the thing is that I have GURPS and Rolemaster if I want that sort of thing. I don't need D&D to be that, I need it to be the game where mighty heroes and wizards lead legions into battle and have castles. It seems like every edition since first has desperately been trying to distance itself from that.