Vyvyan Basterd
Adventurer
The money quote for me is, "if the math works but the game doesn't feel like D&D, we've failed."
The more important quote to me is:
Mike Mearls said:If the system is sound, but it can't replicate D&D's classic adventures or seamlessly support any of D&D's settings, it isn't the right system for D&D.
I'm a fan of 4E and am currently running it. But one of 4E's weak points was replicating something as simple as a pitfall trap. Either you create some weird solo pitfall encounter trap or you give a character or two a minor boo-boo. This may seem like a nitpick, but traps such as these were important challenges while exploring in AD&D.