This has got to be one of my favorite sonic fangames ever.
The game looks absolutely astonishing: The custom sprites are absolutely beautiful (ie the sonic mach speed sprite), The gameplay is on par with mania, and the music.
Oh my GOD the music is fucking incredible.
While there are some cons (lack of collision sometimes, spikes that you couldn't see coming due to going fast, etc) they are absolutely minimal compared to the pros. This is an incredible sonic fangame- hell this is an incredible game in general; and it's only the demo!
Overall: amazing game, on par with mania. And it bops.