Personal Experiences with 4e:
1) brought me back to the game. I hadn't played a true D&D campaign in over 2.5 years at that point, the last one having collapsed due to lack of interest.
2) brought 3 other people back into the game, 2 from the aformentioned campaign, one who had been on a 6 year D&D hiatus.
3) I DMd for the first time. While I had attempted to get a grasp on DMing in 3.x, it always felt out of reach, especially creating unique encounters without breaking EL.
4) I introduced two BRAND NEW players to the game. Neither of them had played a pen and paper RPG before, though like all of us they had a large collection of videogame RPGs. Part of the fun was introducing them to roleplaying a character and solving puzzles in a D&D way (rather than the traditional run around and press A til you find the secret way).
5) About halfway through our play, one of the players got the urge to DM again, he being the DM of our last campaign from 2.5 years previous. As a result, we've played to level 9, that being the highest level I've ever played a campaign to. The highest I ever played to in 3.x before collapse was level 7. I suppose if you rescale for 3.5 vs 4e levels i'll have to hit 10 or 11 to be equivalent, but whatevs.
Now, has it been all sunshine? No, the nature of the two new players being used to playing an RPG for 40-60 hours for 3-4 months has meant that now passed that time limit interest is beginning to wane, and some of the older players, especially regular players of the wizard and cleric, have bemoaned not being ridiculously powerful. Also, as all of our adult schedules get tighter and tighter with people getting sleepier and sleepier, it gets harder to keep people focused, and D&D faces the ever present danger of being replaced with boardgame night. The members of the party that aren't able to make our saturday boardgame geekery would like to push D&D night off in favor of a boardgame night, but are any of those issues besides the power loss 4e specific? Maybe, maybe not.
Overall, I've enjoyed 4e more than any other edition, both in its simplicity of designing as a DM, and in the overall quality of each class's details. Of course, all I can offer is my own personal experience, and none of it will assuage the hurt feelings of people who liked the old edition better, and next month we'll be hearing statistical "proof" again about how much 4e is failing again. Still, I only know what I've experienced myself and among other D&D groups I occasionally compare notes with (both other groups have also gone 4e, and both like it), but it has been overwhelmingly positive for 4e.