I've recently reconsidered my position on 4e, thanks to the poor way some of the ideas I was interested in were handled in Unearthed Arcana. I was always a proponent of the 3-class system (warrior, expert, mage), but in UA the version was rather bland. Thus, I think that if we were to use a 3-class system in 4e, we would need to use that as the baseline, and then provide example classes that have flavor. Thus, we might have just three actual classes, but there'd be 12 different pre-developed classes to choose from.
Expert - Rogue, Bard, Sage, Artificer
Mage - Wizard, Priest, Druid, Psion
Warrior - Knight, Monk, Barbarian, Swashbuckler
I'm a fan of lowering the number of magic items. I don't like the one-shot things like potions and scrolls, because for a DM it's too much book-keeping to keep track of what dozens of dinky items the PCs have. I prefer for items to have more character-specific appeal, so that, instead of being necessary to defeat challenges, they're cool and . . . well, magical. I'd up the cost of magic items substantially, so that most treasure would be spent on mundane things, and so that the magic items you do get are more special.
Right now, magic items define the character in the way that you need magic items, and without your items, you're nothing. I'd rather have them define the character in the way that people might remember you for the one legendary item you have. I mean, in Legend Lore you never have a bard say, "Ah yes, this was one of the 38 hundred potions the great knight Gregor used."
As for skills, we need to reconsider what's realistic and what's good for the game. A +23 climb skill check will almost never matter, because by the time you have a skill check that high, your party can usually fly. Ditto with Jump, Swim, Balance, and even Hide and Move Silently. I'm not sure how they need to be changed, but make high skill modifiers be ridiculously good, so that they still have an impact even in the face of magic spells.
I mean, seriously, who needs Climb or Balance when you can fly? Maybe have Climb give a bonus to grapple checks, and Balance give a bonus to resist Trips and Bull Rushes?