It would be awesome if we just tossed all the grid-like ridiculousness of 4E forever.
No power source. Why are there so many different sources for magic? Shadow, primal, psion, arcane, divine... gimme a break. Likewise, no roles. If the fighter wants to pick up some Lockpicking, what's stopping him? His class, silly. Nuts to that. Give me modularity/versatility, or give me -10 HP.
No daily/encounter powers. Awful, way-too-meta way of balancing the game that annihilates suspension of disbelief. Just tone it all down. Not every fighter needs to be Ichigo or Inu Yasha. I prefer my fighters as salt-of-the-earth type, sword-and-board sluggers who aren't remotely magical in what they do. 4E ruined that for fighters. They all had these... glitzy powers. Lame.
No grid-measurements. Use feet or meters, but not ambiguous "squares". I disliked being relegated to a mat because the rules couldn't handle themselves any other way.
No more DDI. This is a symptom of a disease, namely the fear of being out-shined by the PC game market. D&D is brand-strong, and needs to embrace its pencil-and-paper roots by making a game that's about quick dungeon generation, flexible social and combat conflict resolution, etc. Making your game (and by extension, your game's rules) rely on the internet is basically admitting that your game can't hack it compared to PC games.
Transparency in monster and spell design. I cannot... simply CANNOT stress this enough. Show us how it's done, and make sure when we look in the MM, the numbers actually work out the right way. I was so disheartened by the 4E MM when the damage for monsters wasn't at all like the DMG said.
I have to go, but I'm really... really abraded by the news of 5E, a meere 4 years after 4E. Just... sad and encouraging and I dunno.