Except the expansion arrangements don't sound as good and doesn't save high scores
Daigassou is like a pure rhythm game in that it's all hitting the right notes at the right time. Each direction on Dpad is a "note" and each of the face buttons is a note. On higher difficulty, L shoulder will be used for sharps, and R-trigger will be used for octave changes. The visuals are merely functional. And the music is all midi.
But get past all of that and it's one of the coolest games ever because...
1) You play an instrument part of a song. This means that despite the fact that there are "only" 39? songs in the game, each song has 4-8 different instrument parts to it mean that you actually have HUNDREDS of patterns to play. And different difficulties have different patterns too.
2) It's hard. Ouendan is hard, but it's a different kind of hard. Ouendan is a "train you til you stop failing" kind of hard. Daigassou, OTOH, has some parts that I still cannot do because either I'm not physically coordinated enough or because my mind cannot process the notes that fast. But it's a good thing. Just like Ouendan, the game teaches you to do better at it.
3) Multiplayer is awesomely awesome. If you have other friends with DSes, you just need one cart to host and then everyone else can play & contribute to the song the host chooses. Up to 8 players off one cart. It's the most underrated mp game ever.
4) And if you must have more songs, you can compose your own songs too and save them (and can transmit those by WLAN too for multiplayer).