A shameless attempt at cashing in on the long-dead Guitar Hero/Rock Band craze. The gameplay and angled perspective is an identical clone to Guitar Hero/Rock Band, the artstyle for most of the interface is a shoddy rip-off of Rock Band, the syncing is extremely off with no way to adjust the note timing (you generally have to hit keys VERY early), the rhythms are generally nonsense with respect to what's going on in the music, and the song recognition/leaderboard systems don't seem to work.
If you want a free open-source game of the press-buttons-to-music variety, check out Stepmania or Frets on Fire instead. If you want a game that will automatically generate gameplay on the fly to your music, play Audiosurf instead. Considering the better alternatives available (and that half of said alternatives are free!), Rhythm Zone is absolutely not worth the time or money in any conceivable way.