I like 4e a lot, but I do have some issues, being on both sides of the screen:
-Tiny attack and defense modifiers thrown around--I can keep track alright, but the new players have trouble keeping it all straight and doing the math. Our Ranger took Group Quarry (a conditional +1 to damage), which is frankly too much trouble for too little damage. Maptools games are nice for this.
-Math issues in the base game; Expertise et al. It's not at all hard to see or fix, without inventing new must-have feats. +1 to attacks and NADs at Paragon and Epic is perfectly sufficient.
-I'd like to see non-combat roles, like Face, Acquirer, Planner, or Transporter, added to the game, separate from combat mechanics. Too often, there's little incentive for people to participate outside of combat, and I'd like to make that participation easier and more central to the game.
-Sloooow errata pace. The July stuff was great, where's the Arcane/Divine/Primal Power errata? Believe you me, there's stuff that deserves it. Unfortunately, this is probably related to the quick pace of product release, which I do like a lot.