Soooooo many:
1) sound - it's stellar
2) styles - they're so believable
3) vocal processor - the best in the biz
4) look/feel - it's a slim, trim, sexy beast
5) chord sequencer - fun, fun, fun
6) 4 outputs, and the mic effects follow the mic wherever you send it
7) touch screen - like having an iPad on the job
8) dual media player - has NEVER, ever glitched or hiccuped on me.
9) best multitasking unit out there - I tweak, move, save, write ... all while playing live.
10) fantastic support with updates and freebees.