The $80 PC bundle is cheaper than any other version of the game, but it includes the Xplorer guitar bundled with the Xbox 360 version of Guitar Hero II, rather than the updated axe modeled after a Gibson Les Paul that comes with the console versions of Guitar Hero III. This certainly isn't a deal-breaker, but the updated guitar feels markedly better than the Xplorer.
As you'd expect, playing Guitar Hero III on the PC with the Xplorer guitar feels the same as it always did. It's still fun. One of the draws of the PC version is the promise of portable play via notebook PC, making use of the alternate keyboard controls to avoid transporting the unwieldy plastic six-string. Though there are two default setups for keyboard control, and both work well--one using a keyboard-mouse combination and one using keys exclusively--neither effectively captures the essence of Guitar Hero's real-life guitar-emulating enjoyability.
Assuming you have access to a mouse when you're on the road, the mouse-and-keyboard control combo feels much better than the keyboard alone, mainly because you're performing separate actions with each hand. Using keys to press frets and other keys to strum feels like, well, pressing keys on a keyboard while holding down other keys on a keyboard. Having one hand on the keys and the other on the mouse makes the disparate actions of strumming and fret-pressing at least tangible, if not mechanically accurate.
The mouse's left and right buttons correspond to up and downstrokes on the guitar, with the middle mouse button serving as star power, and horizontal jiggling of the mouse initiating whammy bar action. Having the strumming actions assigned to the two fast-clicking buttons of a mouse actually affords more control than even the plastic guitar in this regard. I haven't mastered both upstrokes and downstrokes on the guitar controller, but I was able to do both with ease using the mouse. Moving the mouse back and forth horizontally for the whammy bar also felt fairly natural, and was again actually more convenient than using the real whammy bar of the plastic peripheral.
Despite the enhanced strumming control of the mouse, using the keyboard to press frets felt unnatural, and medium songs that I've played before with ease using the guitar peripheral were a challenge to get through. Pressing multiple keys at once for chords was most problematic due to the small size of the keys on a typical keyboard. Depending on your keyboard-related dexterity, you could certainly get used to playing the game this way, but there's not really an incentive to do so--it's just more fun to emulate real guitar playing with the plastic instrument.
If you've only got a PC or Mac, buying Aspyr's version of Guitar Hero III is an easy choice, especially at its lower price point. But even taking this affordability into consideration, it doesn't make sense to buy this version over the full-featured Xbox 360 one unless you've got a huge monitor and don't care about the uncertainty with downloadable content. For the megamonitor-endowed with a different console, the better matchmaking courtesy of Demonware make the PC version a better choice than the PlayStation 3 iteration with its barebones online play, and downloadable content is certainly more likely for the PC than the content-less Wii version.
Though the choice of versions is yours, you will have no choice when it comes to rocking. Choosing to not rock is not acceptable.
Guitar Hero III: Legends of Rock comes to PC on November 12, shortly after the console versions on October 28. Though Mac support won't be included at first, the retail edition will be both PC and Mac compatible at a future date, hopefully later this year.