If your system is up to it, Guitar Hero III for PC is just as great, if not greater, than it's console counterparts.
As usual, the songs are amazing, but this time they seem to be significantly harder than previous versions, and you have to be pretty awesome and practice quite a bit to play most of the songs 90%+ on Expert. The hammer-ons have been improved significantly, and I can trust them to the point that I use them all the time.
Career mode is fun and challenging, even if it's the same thing it has always been, aside from the 3 boss battles. The bosses are disappointingly easy to beat up (easier than almost all of the songs) until the final battle on hard, which is extremely difficult for me, even though I can play most of the songs on Expert very well. I still haven't beaten it. The fact that you can't practice boss battle songs (not yet at least, the Xbox 360 version just released practice-able versions of the boss battles) doesn't help either.
What really is going to make this game special is the user-created downloadable content that is going to be available for the PC version. Within a few months, I'm sure someone is going to crack this game and start pumping out custom songs, and we'll be the first to have them before anyone with a console. Online play is also going to be great, because it's free, although no one really seems to be online yet. The online leaderboards are fun to look at too, although I'm sure my scores won't be up there for long after more people start buying this game.
I would highly recommend this game to any PC gamer. If you've got the hardware and you aren't afraid to shell out the $80, go for it.
PS: If you ever play online with S-Factor, that be me.
PSS: Have fun playing "Raining Blood" on anything higher than Medium.
PSSS: "Through the Fire and Flames" isn't the only song in this game. When you play online, don't be a jerk and pick it if it's a best-of-three duel. It's too damn long.