Codemasters' new rhythm action game, based on American Idol, attempts to combine the timing-based, performance-emulating mechanics of games like Parappa the Rapper with the pageantry of entertainment mastermind Simon Cowell's feverishly popular reality TV series. Neither of these facets of American Idol is executed quite right, thus producing a game that's built on compromise.

American Idol flagrantly steals its main gameplay mechanic from Gitaroo Man.
The action in American Idol is directly derivative of mechanics found in Koei's inspired rhythm action game Gitaroo Man. However, the mechanics lifted from Gitaroo Man represent only a portion of that title's gameplay system, and they were better implemented in Gitaroo Man as well. In American Idol, you're presented with a cross in the center of the screen, while in the background you're shown an avatar who is crooning the song. Button commands move from the tips of the cross toward the center, and the closer the icon is to the center of the cross when you press the button, the better your avatar's singing will be. Inversely, if you screw up and your timing's off, the singing will falter by going off-key and losing its timing. The bad singing is done really well by making it apparent when you're not playing right. The gameplay is fairly simplistic, with all of the action occurring on the face buttons of your controller, though it'll regularly throw you some curves. The speed and complexity of the button commands can get pretty rough in the expert difficulty level, but even then the judges are pretty forgiving, so you really have to butcher a song pretty badly not to win. The game also supports a Dance Dance Revolution-style dance mat, though this mode is ridiculously easy. American Idol's gameplay is shallow and easy, and, unfortunately, the game doesn't have much to compensate for this.
The heart of American Idol is the competition mode, where you create your own American Idol contestant with aspirations of being the new Kelly Clarkson or Ruben Studdard. You'll start in the audition room, move to the theater, and finally end up on the American Idol stage. Unfortunately, the gameplay remains the same the entire time. So, basically, you perform a song, listen to critiques from the judges, and then repeat. Since you'll be on "TV," your appearance factors in to how well your performance is received, so American Idol includes a little dress-up mode where you can choose a variety of different outfits. You're given a rating on your apparel after finishing a song, but how that rating actually weighs in to the judging process is unclear.
There are several other options beyond the main competition mode in American Idol, but they are all pure filler. The rehearsal mode lets you try out songs without being judged. The party mode lets you and some friends each take a crack at a song; then you get to judge the other players' performances, which--with the people who are singing also doing the judging--seems like it could get really political really fast. The karaoke mode barely counts as a game. You're presented with a lyric-less version of one of the songs, and the lyrics are presented at the bottom of the screen. At the end of the song, there's an option to "judge" the performance, after which you're dumped back to the menu screen. Finally, the jukebox mode lets you listen to the game's amateur renditions of the pop songs featured on the soundtrack, which seems a bit pointless. If you wanted to hear these songs, wouldn't you just go listen to the originals?