Honestly, having played with both, I greatly prefer 4e over 3.5.
3.5 is nothing but various levels and flavours of broken-to-the-point-of-unplayability, with absurd power creep, class imbalance, and lack of round-to-round choices in combat.
4e, on the other hand has a good, level playing field, and, from what I've seen, doesn't power creep too much, which was 3.5's primary problem (Aside from full casters. Goddess, casters! What did us mundanes ever do to you?).
The people who complain about there being less outside-of-combat stuff to do are jesting at scars that have and will never feel a wound. I've spent more time enjoying 4e outside of combat than I have enjoying 3.5 in OR outside of combat. Their narrative skills (or their DM's narrative skills) may have trouble adapting to things without a strict ruleset, but there's still no reason you can't stab the bartender, he just doesn't have a page and a half of stats for the DM to run crying to.
Perhaps most importantly, 4e made it fun to play as a frickin' caster again.
Yes, I'm aware that all classes are, mechanically, just as caster as each other, but in 3.x you had mammoth spell lists, planning and preparing your spells, followed up by the DM pulling a TPK out of his arse because you had the gall to not play a batman or a CoDzilla.
In 4e, you have your powers, and no save-or-sucks, no save-or-dies, and no batmanning your way through the fight and leaving everybody who rolled lower on initiative (which is everybody, thanks to your quickened Celerity spell you've had ready to cast as a free action since you woke up) standing around feeling impotent.
4e is an actual game, 3.5 is swinging around big numerical sticks and pretending like they mean a damn.
