Nice level, I really liked it. The collectibles were well placed, and the clouds in the skybox looked particularly nice and added some uniqueness to an otherwise familiar-looking level. I also thought that the breakable pillars that dropped the rock was cool, and the part on the minecart where you drive into the sun for a second before going down the slope is pretty.
One thing I have to say is that the exits of the two paths after the first path split have their exits facing each other, which makes it easy to go down the wrong path backwards, especially if you take the minecart path like I did. I actually got lost by going in a circle back to near the beginning, and it took me a couple minutes to figure out where to go to continue past the area the paths meet. However, later in the level near the end, you do a super fantastic job of discouraging the player from going backwards down the road not taken by using the explosives to blow up the wall on one, and cacti the player launches over on the other. It was so natural, I didn't even notice at first that two paths were coming together, which is perfect. When exiting the path from the explosive side though, the slope the player lands on his pointing down, and players will probably take the path of least resistance, which is turning right down the slope to get to the cacti instead of turning left up the slope to continue forward in the level. This is ok I think because since the player is unlikely to go backwards in the level through the cacti, but usually leading the player to a dead end should be avoided, because it can potentially confuse the player, and make them stop and turn around for no reason.
Circling back to the topic of the beginning path split where I took a wrong turn, it might be hard to make it more clear for the player where they should go at the end of the first path split near the beginning of the level without changing the level layout too much, but one possible way could be to break a pillar holding up a rock with dynamite on it to break a wall at the end of the not-minecart path, arid canyon act 1 style. This would definitely change the flow/pacing of the level though, which may not be what you want.
To add to what Othius and Nuhu said about set pieces, I think that knocking down a pillar that supports the ceiling of a tunnel with a minecart, and then having to dodge/jump over falling rocks while in the minecart for a brief moment could be a cool ending sequence that draws on and combines what was in the rest of the level, but the current ending is good as it is too.
When I thought I saw everything the level had to offer, I enjoyed finding and playing the slightly hidden knuckles path and was like "wow, there's more!" Some things I noticed is that the first room is inconsistent with which walls are climbable, which might be an oversight. Also, I would consider putting unclimbable walls near the path's exit to deter players who haven't been through the knuckles path before from thinking that its exit is an entrance. I would also consider that if the player is playing as knuckles, and also holds forwards after being launched from the diagonal spring that is across from the exit, they will be able to enter backwards through the knuckles path's exit easily.
Overall a cool level, thank you for making and sharing it!
