I finally picked this up a few days ago, just got around to playing it today. Man, this game is like crack. As others have mentioned, it's got a great progression system to keep you hooked, the quests are fun little goals to set for yourself, the unlock system is pretty easy to deal with, and of course the music is amazing.
I will say, out of all the note types, the wavy holds with the directional release at the end are fucking me up.
I can't imagine how hard this game gets at harder difficulties, depending on the song, I have a tough time keeping up on "basic" mode. I'm not the rhythm game expert that I used to be back in my guitar hero days, that much is for sure.
Though, I do feel that (at least in basic), the notes don't always match up with the songs perfectly, so it leads to some awkward presses. Usually that kind of thing works itself out the higher in difficulty you go, in other games.
Shame they went for that fuckin artstyle. It reminds me of how much I hated the Link's Awakening remake art.