WOW. There's a lot of votes for Vancian Magic. I thought I might be part of a small minority in voting for it. But yeah, I'm overall pretty happy with the current incarnation of D&D. The magic system is much the same as it always has been, and as such, I really don't have that big of a problem with it. However, I think that something more interseting and useful could perhaps come along, while still keeping the flavor of the game intact. I'm fond of classes/levels and hitpoints. It keeps D&D from being ultra-realistic, and simplifies things for teaching thigns to new and casual players. Hours of picking skills to "create your own class" is tiresome, even for a guy like me that enjoys throwing together characters.
If something must go for the next edition, then the magic system can be it.