Okay, I played it and HOLY CRAP IT'S...
good for a fan game, but this constant comparing to Sonic 1-4 needs to stop. It emulates the classic gameplay which in itself really isn't that big of an accomplishment. Who developed the original Sonic physics? Sonic Team. Who emulated those same physics again and again for more than 15 years? Sonic fans. Now if the guy one upped the existing physics, bringing something new to the table gameplay wise, I think the game would be worthy of comparison to 1-4. But as it is, it's Sonic 2 gameplay with a few issues. I don't mean to sound like I'm hating on the guy's work, he did a good job, but I really can't see why people are raving for something that has already existed 19 years ago. Skilled painters can reproduce the Mona Lisa, but does that make them worthy of da Vinci levels of praise?
Really it all comes down to the visuals that deserve the most attention, as this is the area that the game designer spent a majority of their time. I'll admit, they're impressive for a fan work, but as I've stated all over the topic, they simply do not have that Sonic spirit seen in the official games. The game shares more with Vectorman or Rayman 1 than with Sonic. It's a cool reinterpretation, like seeing The Simpsons drawn in an anime style. Cool to see, but not an evolution of the existing style by any means. I'd rate it an "A" compared to the dozens (hundreds) of fan produced sprite-based games. But compared to 1-4 I'd rate it a "C".