How they work is two guitar players will go into a duel and play parts of a song back and forth.  You can earn power-ups as you play through the areas of the song.  By tilting the guitar upward you can send those power-ups or attacks over to your enemy.  The idea is to drain your enemies meter and win the battle.  In career mode if you do not win the battle before the end of the song you will lose.  In multiplayer and online modes you will go into a sudden death round.

There are also exclusive recordings which were done just for Guitar Hero III.  These come from the likes of Tom Morello from Rage Against the Machine as well as Slash from Guns N’ Roses.  These are for the battle mode specifically and make this mode very worthy of being in Guitar Hero III and in future versions.

Other nice features include the practice mode.  This allows you to go through any song and begin it and end it from any spot which you like.  If you are having trouble with a difficult solo or something of that nature you can start the song right at that point.  You can then play it at the same speed or slower speeds so that you can get it down without having to worry about failing it over and over again.

The difficulty is a bit of a concern with Guitar Hero III: Legends of Rock.  The game seems a bit too easy on the Hard difficulty until you get to the final string of songs in career mode.  When you play Guitar Hero it should be extremely difficult to play songs on the Expert difficulty.  I would consider myself a slightly above-average player at Guitar Hero and I was able to go through the first 8 or so songs on Expert without failing any of them once.  This is a bit too easy as the songs seem either too easy or too hard.  That may be being a bit nit picky but it must be mentioned.  If you are going to play Guitar Hero on expert the songs should be hard enough that you can’t beat them on the first try I feel.