I find Weclock's joke like idea of using a guitar as a controller in that way rather creative, and something I may look into.
Different 'controllers' work rather well. I've made good use of a Graphire.3 tablet for playing a few RTS games and X3:Reunion. Very low level, but a guitar or a motion-sensor setup could be the holiday project.

Earthworm Jims are mine. Second Sight is a great game but I finished it years ago. Battlechess is temptating...

Second Sight has Starforce though, so if you enjoyed it I really recommend getting the GOG DRM-free release. I know I am.

How is Second Sight a good old game? It was release a mere 3 years ago.
Battlechess, oh man that takes me back.

That could only improve the gameplay as far as i'm concerned. I certainly couldn't make it playable using a mouse and keyboard.
I guess i didn't play it for long enough to really know, but I couldn't recommend it for $5.99 (or for free elsewhere), let alone $9.99. Maybe it gets much better later on.
As for the age, Toca3 is newer. I don't mind newer games being added, especially if they are DRM free versions. But there does seem to be a danger of GOG turning into AOCG.
(any old codemasters games). ;-)
Codemasters has a library of great games that i'd rather see on here.
(All Colin McRae games, Brian Lara games, Dizzy, PoW, Overlord, Micro Machines, Toca2, etc..)