Pretty neat little tech demo, though it's not much more than that sadly.
Some of the changes made to the art style are very jarring as someone who's played Portal 1 and 2 to death. Some changes range from questionable to outright bizarre, as well as some important props just being completely unchanged such as the companion cube which feels incredibly jarring. The game's performance is also less than stellar, barely breaking 10fps with an RTX 3060.
This game is worth trying if you want to waste an hour, but beyond that I don't see it having much lasting appeal besides being a fun little oddity to test how strong your PC is.

Some nitpicks aside, this is the definitive way to play Sonic 1, 2 and CD!

For 3 and Knuckles, I'd still recommend A.I.R due to it having more QoL improvements and customization but overall, this is a stellar compilation with some beautiful 2D animated cutscenes to boot.
My complaints mostly stem from the slightly blurry looking visuals and generally wishing there were more content included, i.e. Knuckles Chaotix, Sonic Spinball, 3D Blast and the 8-bit games.

I feel as though the expensive price tag is definitely questionable and would say to wait for a price drop if you're unsure, but the game does have plenty of additional side content worth playing. In the end, you're receiving 4, technically 5 great games for a moderately expensive price tag and whether or not its worth said price is up to your interpretation.