Awesome Rhythm game that fans of Japanese music or Rhythm games will enjoy. One of the best games I've played on PSP.
Gameplay: It's a rhythm game, what can you expect? You press buttons in accordance to the ones on the screen. You get either Sad, Poor, Safe, Fine, or Perfect. Songs are unlocked by playing through the songs, Each song starts with Easy and Normal difficulty. Beating the song with a Standard or higher will unlock Hard, and beating the song on hard with standard will unlock extreme for the specific song. You can choose your favorite vocaloid to sing, but the voice will correspond to whoever sings the song you picked originally. You can unlock costumes for the vocaloids, as well as items for the Diva Room, where you can just what the vocaloids do random things and such. The game also comes with a custom track maker, where you can make your own notes to a song you like. I hope you understand Japanese for this though.
Music: Rhythm games are all about the music~! The music is great, many of the popular vocaloid songs for Miku are here, such as Melt. If you like J-pop, you're sure to like these songs. There's many songs to unlock as well, and the Difficulty seems right, depending on what you pick. Extreme is... Extreme, so don't take it lightly.
Graphics: For the PSP, the graphics are pretty awesome, 3D animation, videos that go with the songs, a good techno menu and such. The videos play smoothly, except for the last song on Extreme, which is pure madness, but yea, nice Graphics.
Overall, a VERY fun game that can get you addicted. It's even more fun if you can manage to work out the custom track maker in the game. My Japanese knowledge is very limited, but I still greatly enjoyed this very fun rhythm game. Completely worth buying~