Okay, here's my fix-it-all input:
Not good, but not terrible for a first map, either. I can tell you wanted this to be like a psuedo-sonic adventure action stage. But those types of stages almost never work out right in this game. It ends up getting very boring, very fast.
1) First thing's first. You have to remove those impassable barriers. The expansive cavern theme looks nice and all, but like Torgo said, we shouldn't have to guess whether or not we can jump off a ledge somewhere. Redesign the areas in a way that forces the player to take the route that you want them to. Put like, I don't know, a WALL there, or some kind of hazard.
1.5)Bleh. There's nothing in your level. Nearly no enemies(I managed to see 3), no scenery, nothing. Just a barren, wasteland of a map. Spruce it up a little, make it look more like a cavern and less like a rocky, glowing box with lava at the bottom.
2)You seem to like to torture me for some reason. Why did you make a zoom tube that goes nowhere but to the beginning? The concept was alright, but the execution was horrible. Make it a part of going forward through the stage, if you want to show off so badly.
3)I think you messed up your tags somewhere with the cut-away view. It cuts back to the area I was just in after opening the door. Check your sector tags. Also, give the player more of a clue of what to do in the room with the rising/falling blocks. Nothing sucks more than sitting for 10 minutes, with no idea of how to go forward. Once again, I have no idea why you chose to put that zoom tube there other than to anger me.
4)Long, small hallways with nothing in them but Sonic bumping his head against the walls is not fun. What's the deal, are you afraid of giving the player some breathing room, or something? :/
4.5)Like others have said, try to make a few alternate paths to take. Even if you can only make a 10 second detour, it would definitely make your level a lot more fun to play.
5)further down the long, narrow hallway I come to a dead end, with a small, square lava pool. I think you meant to create a block that rises out of the lava a bit to jump to, but forgot. Anyway, the spring was in there, and I had to end up wading through hot lava to find the yellow spring, forfeiting all the rings I collected. Fix that.
6)All the rest of the stuff wrong with the level is just visual, and not really a big deal. The missing textures here and there can be forgiven.
@Karuno-Don't discourage him from fixing it just because it doesn't meet professional standards. You'll rarely find someone who is able to make amazing maps these days, so you might as well help the people who are willing to learn.