Alright, so imagine you have Sonic 1. Take the momentum, the fun, and the retro charm... and then throw them in the trash.
Sonic the Hedgehog 4, in my opinion, is a pretty heartless, ugly, and artifical game.
Why?
Well, Sonic's 2.5D sprite is overly plastic looking, with a whole bunch of highlights, and not much shading.
Now the level design. Oh boy. It's only Sonic 1 but with different level names and music. Have fun.
In my humble opinion, if you can find another Sonic game nearby, buy that instead. 5/10.