It's designed like a platformer that had sonic mechanics bolted onto it later in development. Too many sections require precise timing and learning stage layouts, which the former isn't conducive to how one typically plays a sonic game and the latter is a real kick in the nuts when the game is extremely thrifty with its 1 ups and continue have to be earned playing that shitty ass bonus stage which sucks ass.
Sonic 2 gets that shit right, yo. Fun stages designed around Sonic's abilities, not too difficult but not easy either, and bonus stages dont make you want to punch your local preacher. Sonic 1 is an interesting start for the series but it feels like the Mega man 1 of the franchise where the sequel refines and improves on the prequel in almost every single facet.