Generally speaking, the GG doesn't have many terrible games. Plenty of mediocre games, granted, but very few truly awful ones. Europe was treated to the pick of crop, pretty much. This was a slightly different case in the US though, where there was a lot of licensed crap released.
The Disney games hold up well (be sure to try the lesser known sequels Mickey Mouse: Legend of Illusion and Donald Duck: Deep Duck Trouble), and so do most of SEGA's first party efforts. Sonic Triple Trouble, Baku Baku Animal, Ristar, Wonder Boy are recommended. Codemasters' games also - Micro Machines, Dizzy, Cosmic Spacehead, etc.
I've always had a soft spot for Mortal Komabat I and II, and also Marco's Magic Football - very impressive visually for an 8-bit title
If you don't mind opening your wallet, imports Gunstar Heroes and Mega Man are worth keeping an eye out for too.