Sets the benchmark for music games
You can set it to English the first time you play, and then it may as well be a localized version. I think there is also Japanese, in addition to the default Korean.
This is my favorite series for the PSP, or maybe just gaming in general. If you've played beatmania, you know the sort of intense concentration-and-music trance you can get into playing it. As basically a beatmania clone, this game does it perfectly. I'd actually say that with the polished interface, and high production values of songs and videos, as well as the analog-scratching mechanic, this game does it even better than IIDX. (Oh, and you can PAUSE, and even change falling speed on the fly, even in this first game.)
From a slow 4-button track to a scorching 6+L+R set, this game can get a casual rhythm gamer into it, or surely even satisfy the most hardcore. Great replay value because you can grow into different sections of the track list as you improve.
So if you have any interest in rhythm gaming, I would recommend this game first and foremost.