I had high hopes for 4E, and it delivered.
I barely even played D&D before 4E, the game was simply too unwieldy. I have a huge Planescape collection I read for recreation, but never used in an actual game. I played a little 3E, but it just didn't click for my group. We're a group of smart guys who couldn't stand the stupid rules. The system was convoluted, the classes were grossly imbalanced, and DM'ing was far too time consuming.
During my group's 3E phase, we'd frequently discuss how we would improve D&D if we were in charge. When we got a hold of the 4E preview books it was as if the WotC had tape recorded our conversations! As a former Planescape fan I was thrilled to see the much improved and usable cosmology (especially the Elemental Chaos). My only concern with 4E is that they didn't go far enough! For instance, silly holdovers such as alignment still persist (luckily only in a diminished capacity).
4E is an awesome system. I love that teamwork and tactics now matter. However, the class balance was the selling point for me.