This version has plenty of new features to get attention of former users but the feature that made me take a closer look is Drummer and Drum Kit Designer.
According to Apple:
Drummer delivers professionally produced, realistic drum tracks that respond to your direction and can perform millions of unique grooves in rock, alternative, songwriter and R&B genres. Drummer is powered by the performances and sounds of some of the industry’s top session players and recording engineers, including legendary mixer/producer Bob Clearmountain, who has worked with the Rolling Stones, Bruce Springsteen and David Bowie. Designed to work with Drummer, the new Drum Kit Designer plug-in lets you build your own custom kit using a diverse collection of professionally recorded snare drums, toms, hi-hats and cymbals that you can mix, match and fine tune to get the right drum sound for your song.
See it in Action