A bunch of hardcore and talented Sonic fans have created this:
It’s Sonic The Hedgehog 2, but in HD. It’s supposed to be as accurate as possible, but in higher resolution. I like how they left the low resolution floating platform for comparison’s sake. You can try the tech demo yourselves from their site or here:
Sonic 2 HD Tech Demo (8.2 MiB, 735 hits)
I suggest trying the 4X version of the executable first.