I can say that I played Altered Beast when I bought my Genesis and that game quickly collected dust. The game design was horrible. combat was difficult, and progressing through the game was annoyingly challenging, and not enjoyable.
It sucked.
Sonic the Hedgehog was fun, but no Mario. As for Sonic not having slow-down. It had a few places of slow-down. Whenever you several coins that you collected the game slowed down to a crawl, and quickly saw coins disappearing so that it could catch up speed. I didn't mind this too much, because the effect of seeing tons of coins litter the field was awesome during the day.
I remember showing my friends Sonic's attitude for having to wait too long. I thought it was the coolest thing at the time, now I think it is pretty cheesy.
Bubsy the Bobcat had the some great waiting animations though. That is a game I hope shows up on the virtual console...it wasn't great, but it had some charm.