1. Extremely low distortion at the same SPL as other speaker types
2. Very realistic dynamics at both the loud and soft ends, and the loud can be achieved with a very low powered amp, too
3. Clarity, and great transient response, and accurate reproduction of subtle differences in timbre
4. They direct the sound where you want it to go, and keep it from going where you don't.
5. Placement is much easier than other speaker types, which can be much more fussy
6. Easier to drive - you can drive them with pretty much any amp you want
7. Very life-like presentation - you can feel the music
About the only negative I can think of is their size, if your room is small.