It was okay. Sonic can be speedy but to many times he had to wait for things to happen. I died more than once because of impatience, and that is an interesting reaction to give players when you call your character 'Sonic'. Weird level design choices, but i guess that can be forgiven since it's the first game in the series. They were obviously still experimenting. The secret emerald levels felt really weird and the backgrounds in them made me almost puke. It felt a bit tagged on just to create repeatability in an otherwise really short game.
The bossfights were a complete joke and uninspired. The highlights are the art (i can't believe this is from 1991, it looks better than most snes games at the end of the console lifespan). Some nice music tracks, and a few good levels.