It's pretty fun so far. The Quest Medley system seems much better than the Chaos Notes (I think it was called?) from the last game, and the soundtrack has some awesome new additions. I'll definitely be playing a lot more of it in days to come, in order to get my rhythm game fix until Project Diva f 2nd. It's a little weird how they have very few EMS stages anymore, and changed many old ones to FMS stages, but I bet they couldn't fit much video on the cart with SO MANY SONGS.
My only complaint--and one not with the game--is that I still hate how weak the 3DS' sound is with both headphones and speakers. It really bums me out not being able to blare some of these songs and enjoy them fully.