My groups and I love 4e. For us, its simply the best version of D&D so far.
I love it for the ease of preparing a game, for the huge diversity of NPC and monster abilities, for the PoL assumption and new cosmology/background, the electronic resources, and I've always loved using minis during gaming, so 4e scratches my itch perfectly. (I used to and still do build custom terrain and dioramas for gaming, so the minis assumption is a big plus for me).
My players love it for the variety of classes and character types they can play, where one character of a given class truly plays and feels different than another. They also love the fact that powers for all classes work the same way (yep, I know some folks hate that, but my players don't want to have to learn four or five different subsystems to play different classes). They like that PCs don't start out so fragile, and don't reach god-murdering power as they did in previous editions.
The few things that did bug me about 4e were no long-term injury rules, few non-combat powers, and magic items feeling rather mundane were things we easily houseruled or added to the system.