Rapstar is essentially a rap themed karaoke game. The game will use radio versions of all its tracks to secure a T rating by the ESRB. That said players won't be penalized for cursing but this is by no means necessary.
There are two modes, either Career or Party modes. The Career mode is in five stages. Each stage has eight tracks for the player to master, including a New Song Challenge which is unlocked as the player progresses through the stage. The Party mode allows players to simply pick an individual song and perform it
I saw this in two different HMVs (Bolton Middlebrook and Wigan Grand Arcade) and it's £10 on the 360. I'm tempted to buy it myself, this deal was posted for the PS3 version earlier in the week but i didn't see it myself.