I love my guitar hero. I was really happy with the song selection in guitar hero 2, and the difficulty level... Guitar hero 3 is really thrash-centric, I enjoyed the melodics in gh2. However there are a lot of amazing songs in GH3, 3's & 7's, Impulse, One, Through the Fire and Flames, The Metal, etc. etc. Real enjoyable songs to listen to and play.
I suggest everyone try it before they buy it though, it's a big investment.