-It's got interesting characters
-The fight scenes are choreographed so well and the jazz-like music in the background mixes so well with the mood
-It has a fairly non-linear plot, so many of the episodes could be watched on their own without missing any important information from the previous episode
-It's got an amazing ending, perhaps one of the best of all time
-It doesn't ever take itself too seriously, but at the same time never attempts to be campy.
-The music tends to be awesome
-A large variety of different episodes; from the serious nature of the last two episodes to the goofy nature of the mushroom episode
I could go on. Let me just end with this: this was one of the first serious anime series that I ever watched (was about 13 or so when I first saw CB) and is still is one of my all-time favorite series.
Bottom line: check out Cowboy Bebop if you haven't. There's a good chance that you'll find at least one thing from this show that you'll really like.
