I loved 3.0 when it first came out. It was the feats, skills, and simple multiclassing. The promise that fighters and rogues would have powers that would be interesting, just like casters had interesting abilities.
As someone said above, it was true for a bit. The multiclassing thing worked well if you were mixing two non-caster classes. I started getting annoyed by 3e when 3.5 came out. Yes, it "fixed" issues with rangers and bards (though Monty's bard was far superior imo), but prestige classes and feats were ran all over like cockroaches on a 3 week old plate of tuna. It was also about this time when I realized that you simply couldn't multiclass as a caster and that fighters were just fighters, though leveling one was more interesting. The problem was your options only came during character generation and leveling. In combat, it was much like previous editions. That said, I had no real problem with 3e as a player - I just figured out what rules I liked and created characters that played to those strengths. One thing truly killed 3e for me though. DMing.
I've been a DM since the game was released in the 70s, and after working on games for mid level characters, I really started to hate the system that I thought I'd love. "Hey, creating monsters is easy! Just pick a base type, level the monster with chart X, add a template, add character levels, pick feats and skills and you're ready to go!" Yeah. It seemed easy enough when I read about the theory, but in practice in annoyed the bajeesus out of me. I pretty rapidly went back to my old 1e method of just making up whatever I wanted. As such, I had basically pitched the monster manual, I made up my own magic items because I didn't like the item creation rules nor all the boring +X items, so the DMG rapidly became useless as well. Basically, the only thing I kept was the classes, and I ended up giving each character special abilities to make up for the lack of true options. So yeah, I was rolling D20 and comparing it to a DC (like a bunch of other games I could name), but it was barely recognizable as 3e.
4e again has put me in the "hopeful" category. We'll see how it plays out, but seeing as how the mechanics for the wizards and warriors are the same, it seems more likely that the two will be more equally enjoyable from an in-game options perspective. We'll see how it all pans out in a couple weeks.