Basically here's how I feel about 4e:
* If it makes D&D more popular, and easier for newbies to get into the game, it's good.
* I like the changes to the races and cosmology (tieflings, dragonborn, etc.), although this isn't a big deal to me anyway.
* The idea of being able to create a balanced party without spellcasters (thanks to Warlords, Second Wind, etc.) is pretty revolutionary and I'm looking forward to seeing how it works.
* I'm really interested in playing it to see how it goes and all the weird combat-related feats and abilities they've added.
That said:
* I mostly play clerics, druids and obscure specialist wizards (necromancers, polymorph abusers, monster-summoning conjurers) so I am disappointed (on an admittedly entirely selfish & personal level) because a lot of my favorite character builds are apparently being nerfed or eliminated from the core rules, 'cause of all the Iron Heroes~Book of Nine Swords mania sweeping the 4th edition design team. Heck, I was already bummed by all the spell changes from 3.0 to 3.5.
* As a DM, I've mostly been running variant forms of D&D and 3rd-party D&D campaign settings for the last four years, so I don't have any immediate interest in switching to 4e because first things first, I JUST GOTTA RUN A "TESTAMENT" CAMPAIGN BEFORE I DIE!!! :/
Another big change in 4e that I really don't like, although I can see why they did it, is the elimination of the "noob" levels. If D&D4e is divided like this:
Level 1-10: Heroic
Level 11-20: Paragon
Level 21-30: Epic
Then D&D3e is divided like this, informally:
Level 1-3: Newbie Adventurer
Level 4-14 or so: Heroic, aka "The Sweet Spot"
Level 15-20+: Chaos; Too High-Powered; Severe Ups & Downs; Weird High-Level Magic Becomes a Virtual Necessity
Frankly, I like the old system. I *LIKE* the fact that D&D games must change, not just in story, but also in strategy & tactical style as you advance. You go from being hapless apprentice adventurers who may have to run from a few hobgoblins to --> heroic adventurers who are pretty dang tough --> to high-level castle-owning, teleporting, plane-shifting dudes who have all kinds of crazy powers at their command but always have to worry about getting brought down by a "finger of death" or prismatic wall or beholder's eye beam or something. (But on the upside, your super-high-level cleric friend can bring you back. Unless the enemy traps your soul in a gem. In which case there's ANOTHER countermeasure you must have. Etc. High-level D&D in 3e and below isn't a game of rushing into danger, it's a game of preparation and gamesmanship with a lot of chaos, hinging on the results of random saving throws.)
To me, all of these different styles of play and have their own advantages and disadvantages. Basically, it's like having multiple games in one -- it's like low-level D&D equals Warhammer FRPG or Runequest, and high-level D&D equals Amber or Exalted or Ars Magica or Dying Earth Archmages! So flexible!!!
I reluctantly understand why Wizards eliminated the "noob" levels, because frankly, it's true, whenever I play D&D with someone who is a newbie hasn't played before, they're always shocked by how weak 1st-level characters are. I played with someone like that just the other night. They're all sayin' stuff like "What?!? I only have 10 hit points?!?" and "What?!? I can only use magic missile 4 times per day?!?" To me, it feels like power creep as everyone wants to play a tougher and tougher and tougher and more "Mary Sue" wish-fulfillmenty high-powered hero. But on the other hand, I realize that i sound like an old geezer complaining "Kids these days... In my day we died at zero hit points and we LIKED it! 'Cause there were no other kinds of RPGs to play!" @_@ In general, though, even in this modern age, I prefer a harsher, tougher D&D game (as long as it's fair, of course... I'm not saying I enjoy the DM killing the players for fun, elementary-school style...)
(Incidentally, one thing I always wondered about 1e and 2e D&D is that, unless I'm mistaken, you almost never hear "15 minute adventuring day" stories about those editions. Since spellcasters had even LESS spells per day in older editions of D&D, wouldn't it make sense that the "adventuring day" would be even shorter? But I suspect that, in fact, people were just playing with a different attitude and didn't abuse this particular aspect as much. Or 3e players are just much more balance-obsessed and/or players of older editions had so many other unbalanced things to deal with that they rarely got around to criticizing this particular thing. I'm sure someone who played more 1e and 2e games could give me anecdotal evidence to the contrary, though.)
Regardless, though, I do hope the 4e rules are written to be able to support (expect?) a different type of tabletop experience based on the characters' level. What I don't want is for the 1st level party to be fighting gnolls and lizard men with exactly the same strategy and general feel as the 25th level party fighting mariliths and baatezu, only with all the numbers bumped up, i.e. +30 to hit instead of +4 to hit.
I suppose this is something the individual DM can bring to the table, but I did grow to enjoy the different expectations that different levels of Pre-4e D&D carried with them -- i.e. Levels 1-3, "You Are Young, Grasshopper, So You Must Be Cautious", Levels 4-14, "Yeah!! We made it through the hard part! Now we're real heroes! Rock on!" and Levels 15+, "Watch as I pull off this insane stunt or cast this weird spell! Now watch as the monster does this even more insane thing! Agggghhhh! The whole party was polymorphed into snails! No, wait, my sub-character I bought with the Leadership feat casts Mass Dispel! No, wait, Antimagic Field! Agghhh!! This is Chaos!"

Ahh, sweet Chaos...
Jason