Hey, feel free to prove me wrong! I'd like to see that background in a future release of Sonic 2 Advanced Edit Canceled, you know.
If I wasn't prepared for people to mess with my work, I wouldn't have submitted it in the first place. If I don't agree with the direction they're taking it in, I'd concisely detail what exactly I feel was like with it, with visual (audio?) examples, and perhaps try and change their annotations in a way that I think looks better. This would go on and on until we reached some sort of compromise.
That's the difference between just making something for yourself and making something for a collaborative project, though—everybody can tweak their fair share until everybody can agree on something. The thing is, all you've said is "this looks wrong" but you haven't pointed out very specific bits that could be changed, in which way they could be changed, or even made quick and dirty mockups of what you think would look better.
I think the ultimate consensus is that, whilst your art is a good base, it could use some improvements. I'm personally liking the improvements so far, as are others, so I think it's fair that you at least try to make some sort of compromise so it can reach its full potential as a level. What you've done looks good for Sonic 1 or even Sonic CD, but the games adopted more sophisticated pixel art as the series progressed. I think that, therefore, it's natural that we try and put as much detail into things as we can manage to a reasonable extent. I don't think the improvements so far are unreasonable; but, as I said, the best thing you can do is make your own changes to the improvements.
You're a great artist, so I totally trust that you could whip something up that works for everyone.