It features at least 1 level from each of the 5 Genesis era Sonic games, each with re-imagined level designs bosses and new remixes of the songs. There's also numerous easter eggs and nods to other elements of Sonic history and other Sega IPs.
Thanks!
Not sure how I want to proceed but I realized I owned Sonic 1 on iOS so I guess I'll play that much myself. Not sure I really want to undertake playing/watching all of them given how much I want to get done in the next few weeks as is, but maybe I'll just play like one a week for a bit.