It's odd to me that several people have said the early Genesis library has aged poorly. To me, it's the late library that sometimes doesn't hold up well, i.e. lots of games (especially Western-developed ones) with digitized graphics that don't play well with the system's relatively low color count, or lazy ports from the SNES. Doom Troopers, X-Perts, Time Killers, Batman Forever...
So many of those cardboard box releases are ugly and don't play well, whereas the early library is full of classics, especially by the end of 1990. Even duds like Osomatsu-Kun look and sound pretty decent. And the sample quality in games like Space Harrier II is surprisingly good.
For me, the problem with the SNES is that I played a lot of the best games as a kid, and I'm not really one to replay games a lot. Sometimes I enjoy the gauzy, pastoral feeling of the system a lot; sometimes I'm in the mood for something crisper and brighter. And I can't stand the SNES packaging, nor the high prices these days.