It's basically guitar hero/rock band etc but you use your own guitar and play the song as it should be played, if you enjoy jamming along to songs or backing tracks then it's pretty cool.
The only problem is the audio lag you get via a HDTV it's very noticable on some TV's which makes the game unplayable.
I went out this morning and bought some speakers, plugged them directly into the HDTV and it seems to have removed most if the lag. It's still there but hardly notice it now.
Oh, the game isn't cheap either. Cost me £52 because they supply the lead you need to plug your guitar into the xbox/ps3