I spent a chunk of the weekend picking through the 1,500 plus iPhone games out currently, as I started pulling together a gift guide for the iPhone. As you can imagine it's quite a challenge to try and find a handful of gems among all of those games. Sure a bunch are shovelware, but there are also quite a few excellent titles.
Take for instance Gameloft's Guitar Rock Tour. The GameLoft-developed title leans heavily on the Guitar Hero franchise for its gameplay mechanics and aesthetic, but it manages to do enough different to make it work on the iPhone that I found it to be quite a bit of fun to play.
The game comes with two instruments to choose from and 17 songs, all of which I suspect are covers. To play through a game using the guitar you just tap your way through the notes on the four-fret guitar as they fall toward you down the neck of the virtual instrument. The songs drop sustained notes and lines of notes at you as well as a number of double notes. If you come across a line of notes you can slide your finger across them as they scroll down. Once you build up enough rock power you can activate the familiar power-up by sliding your finger up the gauge to go into a power-up mode that doubles your points.