Easily the PSP version of Ouendan
You get to play as several characters from the Vocaloid world, and not only Hatsune Miku. So much that each character has its own song. You can unlock more characters as you play through and you can use whichever you choose, not necessarily restricted to the ones they sing.
The second installment of Project DIVA seems to correct a lot of "flaws" from the first game: now you don't have to be so precise when pressing the buttons. There are a couple of different "challenges" now. Instead of just pressing the regular buttons according to the rhythm as indicated on the screen, you may also have to combine the regular buttons plus the directionals. In some occasions, you'll also have to hold down the buttons until the indication is gone. It adds up a little more challenge to the game, but nothing that will make you feel frustrated.
The background is very colorful, with your character dancing according to the song. I missed something like Playstation's Bust a Groove series, where the character missed the steps if you hit the buttons incorrectly. The colors of the animation may sometimes confuse you and one of two times I lost my indicator because I could barely see where it was.
There are several features that can be unlocked during your gameplay: characters, more songs, items for Miku's room and extra outfits. However, if you want to explore the options a little better, some Japanese knowledge would help you a lot.
Overall, a relatively short, but fun game. If you like rhythm games for portable consoles in Ouendan's style, this may be the one for you.