That is great! I did that in college about 1991 timeframe. I always thought using the IIGS on the Commodore Amiga 1084S was just the BEST. The image just seemed bigger and crisper than the Apple RGB monitor and having stereo sound right there from the speakers was wonderful! Had a VCR and a Apple Overlay Card too and that was our dorm room TV for about a year. (That was also one of my first solder hacks building that connector too)
SOMETIMES - I've found that depending on how much ram you have in your IIGS some games would ONLY work if you set it to 1MEG or 2MEG of available ram. To do that just setup the rest of the ram as a ramdisk. I can't remember specifically which games that helped but it seemed to be the issue whether on the Rom 01 or Rom 03's I've did that with.
Something to try at least.