Alright, so I'm playing Emerald Ties (qq more's game) and here are my thoughts on it so far. (About to play the first snow area)
Music is pretty decent, I'm actually a little surprised for a fangame. Perhaps I shouldn't take fangames lightly from now on?
Nice sprite work, appealing animations.
The physics are a little heavy on your initial startup, it's not Sonic 4, but it does make your movements kinda sluggish in a way. Nothing horrible or anything, it's perfectly playable.
Great spinball mechanic, I think this is executed perfectly.
Coming out of water has the right gravity when popping out, and it was nice to see.
Fire shield works well, it goes in a straight line unlike Sonic 3 which causes you to fall, but still nice.
Sonic in a way plays kinda like SMB3 Mario (Not exactly, but I'm using the control as a reference) I think it should be a little more loose like SMW, but decent enough. I guess what I'm saying is more control after you jump in a direction. Like, let's say you hold right direction and jump, but suddenly you want to land on a platform and hold left, Sonic's direction on his initial jump has more control over the handling once you jump, so it's a little harder to get on platforms
Level design is kinda nice, it rewards your quick reactions and isn't cheap.
Loop-de-loops work perfect
Rain could be a little better on the third act, but it was nice to see!
Probably could use a different sound for the text-box chatting, not that I dislike NES sounds or anything. Just a softer tone maybe.
Bubble Shield works decently too.
Nice touch on the second area where you land on the platform and it makes a slight dip.
The spinning platforms (the ones where you do a 360 and then you jump) are fun
As for one solid complaint, at Act 3 of Relic Retreat, I ended up getting to a certain part where the lava starts rising and there are two floating platforms going up and right. I couldn't seem to jump high enough to make the platform on the left side. I didn't die at all until this level, but I lost all my lives trying to get past it. Oddly enough, when I started my file it put me in the snow area so I'm playing that now.
I probably didn't realize something, but yeah. However, I did like how that part of the level was S3-esque, and before that part I was having fun with the level.
Either way, I haven't played a lot of fangames, but this is my favorite one so far and I'll go work on beating the rest now.