To be honest, the GUS regarding games is only good for Lemmings 3 (uses it's own patch set) and any games that use music modules, such as Epic Pinball, Pinball Dreams and Pinball Fantasies. There are several others, too.
The GUS was mostly used for the demoscene - Fast Tracker 2, Scream Tracker 3, Orpheus and Impulse Tracker all support the card natively (although Impulse Tracker will lack features such as the filters, as the GUS isn't capable of producing these in hardware). Basically, it was used more for producing music than playing games.
Within your post, you refer to the Gravis soundcard as "the GUS" - do you mean either the GUS Classic/Max or the GUS PnP, or perhaps both?
I think the GUS Classic/Max was a good gaming card, IMHO.
