Classic D&D: Designed to be fun
AD&D: Designed to be fun for everyone (spawning a multitude of conflicting and contradictory rules as a result)
3e D&D: Designed to be fun for the player (but a planning and preparation headache for the GM)
4e D&D: Designed to be fun for the GM (but players now feel restricted after all that 3e freedom, by-the-nose combat Powers and final transition into being a boardgame)
5e D&D: Screw it. Let’s play Mutants & Masterminds instead
That’s my experience. In short: GMs love 4e D&D because of the much shortened prep-time, simple NPC and monster creation and easy Monster and Encounter creation rules, but players are less than enthused.