4e is my groups favorite version of D&D so far, hands down. Its simple to play and prep, gives players lots of options without bogging the game down, and gives all classes something interesting to do, in and out of combat.
My DMing style tends to shine most in less rules-dense systems, and 4e is a HUGE improvement over 3e in that regard. Combat is also a big improvement- it moves a lot faster for us, and doesn't dominate as much playtime, leaving more time for investigation and roleplaying. Contrary to what some folks are saying here, 4e has encouraged my players to be far more creative in combat, and describe their actions in detail so it doesn't feel like a boardgame to us (some of my players even "reskin" their powers to fit closer to their character concept). 4e also tends to be less item and gear dependent (and what items there are are not as powerful as previous edition magic items), which lets me run a lower magic campaign setting focusing on investigation and horror elements more easily than other editions.
Finally, 4e has brought 3 new people into gaming in my group that refused to play 3e. Two of them thought 3e was too complex, and one tried to start playing, but was put off by the ordeal of character creation. Now all three of these ladies are playing 4e happily and loving it. Thats a big factor- when the system isn't a barrier to new players. If 3e is even brought up during our gaming sessions, eyes are rolled and some boos and hisses aren't uncommon. My group would never go back to 3e- for us, its simply nowhere near as much fun as 4e.