I've got a few thoughts on 4th Edition Dungeons and Dragons, not for people who have never played it, but for people who have. I played in a campaign (all thirty levels) as an Eladrin Ranger, dying once, coming back (sort of), dying again, and coming back a third time for the final finish. I have to say that I don't like this new edition. I even have to say that it's not really Dungeons & Dragons.
Brief background: I played AD&D extensively back in the day, 2nd Edition AD&D in a couple of campaigns, and one 3rd Edition campaign.
I've never DMed a 4th Edition game and never read any of its official books other than the Player's Handbook - and even that, not cover to cover, though I've read a lot of entries in the online Compendium for the game. So I speak out of a lengthy, but rather limited, experience with 4th.
When I say that it isn't D&D, that's not necessarily a bad thing. D&D was the first RPG I ever played, and has a certain place in my heart because of that. But it's never, in any of its incarnations, been anywhere near what I'd call a solid system for playing generic fantasy campaigns (though, to its credit, 4th Edition comes a little closer). I was always frustrated that I couldn't play magic-using characters that felt like the sort of characters I read about in my favorite books. (I loved Rolemaster for precisely that reason, though I'd now consider it to be too much work for what you get.) Even now, the Vancian system isn't gone. The slots-per-day (indeed, slots fixed with but a single power) mechanic is now just diluted throughout the classes. D&D has been, however, a great system (or set of systems) for playing, well, D&D. The fellows over at The RPG Haven Podcast (and others, too) have commented that D&D is basically its own genre. Bingo. The reality is that D&D is a thing all its own. And that's okay.
But I'm confident that, as a game, 4th isn't really the same as earlier editions in that it's not backwards-compatible. As a rule, you can't really convert characters from prior editions without basically re-imagining them. Again, not a bad thing in itself. If I have any gripe here, it's that you're not really getting what's on the box, red or otherwise. It's made a lot of people really angry, and I understand why. I was more disappointed than angry. I hoped for fixes to a venerable system that would make all those books and movies that I loved finally playable, but instead I got a thoroughly new system, pretending to be the old one.
Indeed, I got a new system of rather more limited scope. Like so many players of earlier editions, I loved the flexibility in character design that surfaced as the game matured into its 3rd edition. Sadly, I never really got to enjoy it, but I did get to see much of that customizability simply evaporate in 4th. A step backwards, in my book.
In regard to its handing of classes, I heard the word "pigeon-holing" being tossed around a lot after the game's release, and I heartily agree. Most mages I've wanted to play in editions past were not Controllers and most fighters I played were by no means Defenders. That kind of oversimplification drives me crazy. The four roles are actually a nice way of thinking about what you want your character to do in combat*, but those roles can be filled, to varying degrees, by multiple classes. It's not a one-to-one correspondence. They've moved away from this somewhat in the new Essentials line-up, and that's a good thing.
If any given RPG has both Role-Playing and Gaming aspects, 4th Edition leans heavily in the direction of Game and is thoroughly combat-centric - more fantasy wargame than fantasy role-playing game. I saw plenty of role-playing around the table in the campaign that I was a part of, but it was really kind of optional. Which was good, because I rarely had the energy for it. Mostly, I just created a character that did his part in a fight and was easy to play. I was really there more to be with friends than anything else.
As I say, 4th Edition isn't D&D. It's D&D-ish - but then, so are a lot of games. You can play the various pre-4th D&D settings, races, and classes with, say, BRP or Hero or even Mutants & Masterminds. 4th Ed is, however, an official product, released by sort-of-the-same folks who gave us the 3.x editions. So I've given in to my more cynical side, calling it 1st Edition "Ish" - up until now, mostly to myself.
Hey, it's not a bad game. I've had fun (sometimes a lot of fun) playing it! Not much more to say on this one. If you have a good time with 4th, by all means keep right on rockin' with it. I can't say I'll never play it again. I wouldn't mind playing the occasional session sometime in the future. It's very much like 1st Edition was for me, in that I played it because that's what everybody else was hankering to play. :) But for what I'm looking for, there are better games out there.
*If you want to see a more adequate list of party roles, a list not quite so combat-obsessed, look at Crafty Game's Fantasy Craft. Although I'm not so much into the class-and-level thing any more, this is a system I'd gladly play as my go-to fantasy system, no reservations. Very nicely done.