Okay, since our feedback session on IRC got cut short kind of abruptly, let me put down a few thoughts:
I still find Sonic's (Jasper's too) special ability absolutely infuriating. Yes, being able to defeat enemies easily is useful, especially since there are a LOT of enemies in your level, but it comes at the cost of having pretty much no mid-air maneuverability. In fact, should I try to thok during a jump for whatever reason, my entire momentum will be cancelled. So whenever there's no enemies around, my special ability isn't just worthless, I'm actually worse off for using it. That's not a good game mechanic. On top of that, there are a few very wide gaps to cross in your level (including one that I don't think is clearable without a spindash jump), which makes it even more frustrating that I don't have any way of building up momentum aside from taking a running jump (which is often difficult because there isn't a lot of space for that and the little space there is tends to have slippery ice on it). And since your level is very vertical, messing up a jump usually means I get to repeat the last 15-30 seconds of gameplay, only to potentially mess up again. That can make your level very frustrating.
My next pet peeve is the ring-drain water, which I always thought was a pointless mechanic. By the time I've found my way out of the water, chances are I'm already out of rings, so it doesn't really make a difference is my rings are slowly depleted one by one or taken all at once. And once I'm out of the water, I'll just pick up the nearest ring I can find and act like nothing happened. The ring-drain effect doesn't actually make a practical difference to how your level plays. It doesn't add anything to your level that regular water would lack, especially not any additional challenge (unless you have the bad luck of being sniped by a pop-up turret before you can grab a ring, in which case you'll probably feel cheated rather than challenged). I think you should bring back the quicksand that was previously there and change Sonic's homing attack to the one that comes with SRB2 (i.e. the one that lets you thok normally when there's no enemy nearby). Or just design a level around SRB2's default characters for a change?
The next issue is that as the level goes on, I increasingly feel that you're just bombarding me with projectiles in lieu of any actual content. That multi-bullet turret in particular doesn't work at all. It just shoots bullet after bullet and never stops, and the only way to destroy it is to run up to it and hope that I'm lucky enough not to get hit. There's practically no way to dodge its shots aside from staying out of its range, which is of course impossible due to the way you're using them. Even worse is the large room with the lava in it, especially on floor level. There's absolutely no structure here, just a bunch of platforms over lava with no clear path forward and bullets coming from every which way. This is incredibly frustrating, not to mention confusing, because on top of not knowing where to go, I'm also constantly hit by projectiles whose source I can't even locate. It's not as bad in the higher parts of that room - on the other path - but even there are spots where I feel like I'm just rushing through your level as fast as I can to avoid all those annoying bullets and flames and whatnot. Your level could be ERZ2-quality otherwise, I still wouldn't be able to enjoy it like. So bottom line, place less enemies, and where you do place them, place them strategically.
Last but definitely not least, gimmicks. This is a recurring problem with your levels: They have a lot of gimmicks, but they're rarely executed in a particularly interesting way. Case in point: The snailers that shoot stepping stones. It's not enough to say "I'm gonna have snailers that shoot stepping stones, and that will be my gimmick". That's the easy part. The hard part, and the more important one, is integrating that gimmick into your level. You need to create interesting situations for the gimmick to be used in. Situations that pose a challenge to the player beyond the basic premise, and that - if you're really good - take them by surprise because they didn't expect the gimmick to be used in that way. The ability to use gimmicks in creative and novel ways rather than just the most obvious and basic ones is what separates an average level designer from an exceptional one, and that's what will make people enjoy your level.
I'm probably just blabbing on and on here, so let me give you a specific example: One of the gimmicks you use in your level are the snailers that shoot flames in regular intervals. I don't know whether that's intentional or not, but they're very similar to the flamethrowing gargoyles in Azure Temple Zone. But observe the difference between the way your level uses them and the way ATZ uses them: Mystic builds something like 50% or even more of a pretty long level around just that one gimmick. Why does it work? Because he constantly finds new ways of using the same idea. In your level, it feels more like "hey, let's put a row of flamethrowing snailers here" and that's about as far as you go with it. I'm not saying that you should copy Mystic's ideas from ATZ, but look at the difference between that level and yours, and try to understand what exactly it is that makes ATZ better.
One spot in your level where I felt like you were trying something beyond the most basic approach with one of your gimmicks occurred where you had two gray snailers opposite each other and next to a high ledge with an extra life or something on it. And to reach it, you had to get the two snailers to stack their stepping stones on top of each other so you could make the jump. That was a clever idea, and that's exactly the kind of thing that will make your level entertaining, which of course should be your primary goal. This wasn't by any means the only interesting spot in your level, there were several things that I found entertaining (or would have found entertaining if they weren't plagued by unrelated issues, like the projectile spam I mentioned above), but I'm gonna be a bit mean here and leave it to yourself to figure out which parts you think might be the most interesting ones.
Related to this issue, I think you should throw out all the gimmicks you don't really need. I already mentioned the ring-drain water, but another one that I felt was absolutely tacked on and pointless was the factory section with the lasers. Not only does it pretty much have nothing to do with the rest of your level thematically, it's also something we've seen a million times in custom and official levels alike, and your level gains nothing from doing the same old thing again. And of course, in case I wasn't clear on this above: Don't repeat the same idea twice in the same level. I already said above that what makes a level entertaining is using the same gimmick in different ways, but there are times when a gimmick just doesn't have the potential for that (or maybe it does, but you can't think of anything). That's fine, you don't have to exhaust every idea to its breaking point. But if you can't put a new spin on something, then don't just repeat it, because that will only bore the player.
There are millions of other things I'd like to talk about in your level, but I think this is a big enough wall of text already. There's one more thing I'd like to say however: If I'm not mistaken, you explicit tried in this level to make the design more open and natural, and less "corridor with stuff in it" like your previous levels. That definitely worked, and it makes a huge difference (to the positive, of course).