What needs to be changed for 4th Edition (IMHO):
1) Feats should be removed from the core rules, and made an optional rule. The inclusion of feats as a necessary part of the game has created a gross amount of power creep, and made the game needlessly complicated to run. Every feat represents an exception to the rules, and ultimately defeats the whole point of d20 as an elegant solution to the messy, contradictary rules of previous editions.
2) Skills should be made broader, more simple, and optional.
3) Reduce the complexity and power level of monters, so masses of magic items and bizarre feats are no longer required to defeat them. I like to see a return to stat blocks that human beings can reasonably create in their spare time. When even WOTC frequently gets their stat blocks wrong, something is VERY WRONG with the game. Also, eliminate the truly stupid and incoherant monsters with wide ranges of unconnected powers, that exist only to provide challanges to to the grossly over-powered characters the rules produce.
4) Get back to archetypical character abilities and roles. New players should recognize the player classes from history, literature and movies. This aids role playing, and cuts down on the time it takes to create characters. Rule of thumb: if the name of a character class doesn't tell the average person what that class can do, it's not archetypical.
5) NO MORE SPIKY ANYTHING! ALL ILLUSTRATIONS WILL FEATURE REALISTICALLY-SIZED WEAPONS THAT CAN ACTUALLY BE USED BY HUMANOIDS! NO MORE DOUBLE WEAPONS THAT WOULD KILL ANYONE THAT USED THEM! AND GODDAMMIT, ELVES ARE SUPPOSED TO BE PRETTY, NOT BUG-EYED ALIENS!