For the song list alone you might buy it. GH1 and 2 are better.
The game doesn't seem to paly as well as GH2; the game has frozen a few times too. The screen is harder to see; the notes are harder to play; the notes move more quickly; the power ups seem to be in more tricky riffs.
So if you're wanting to know about Guitar Hero the series, I'd looking into buying the first or second installments; this one has gone a bit too flash - the graphics have tuned up a bit and maybe over work the old PS2.
On the up side the Wireless controller is great. Buttons are very subtle and not too clicky.
Lefty option still remains.
The new challenges at the end of each section are a bit silly. Why on earth you'd want to face off and jam against some otehr dude thats playing some crazy made up jamming of notes, is beyond me. This game is supposed to be about playing guitar... not beat the Boss.