Your game is really nice and almost feel finished, there's really good things in it, you can be proud!
Here's a list of things I saw:
It reminds me of escape goat. Did you play it? Athough it just feels like an inspiration, it's not bad for the game and can be good actually. I Didn't play escape goat yet, though.
Your game is a bit slow on my computer. And my computer is not a totally bad computer, it's kinda fine, I can usually play, so.. maybe you should make your code a bit faster (was running your game at like 20-25fps. It's fine for playing, but for the moments when you have to go back to your soul before you hit the spikes, it has been really frustrating. I'm not sure about this mechanic by the way. It frustrated me a lot and I didn't find it interesting so much.. )
I think you're giving too much Textual information to the player. Your game should have none or almost.
I have a bit of a problem with how the guy is jumping. Cause sometime he jumps lower and I don't understand why and it's frustrating. (when I'm not moving maybe. But I don't see why it would do that?)
The mechanic of "if your soul hits the spike it will not die" is not really intuitive I think. I'll talk about that a bit more when I'll talk about lvls, but it's a problem.
You have a little buggy thing with the respawn: If you create a soul and then die, the soul stays in place. (Or did you want that? it feels like it's a bug.)
So, I'm just going to talk about each lvl individually, it will be more easy and more clear for you to fix things:
On the first lvl: the thing of putting a switch in the way, to make the player notice that it makes the rocks fall is good. But it's useless for the gameplay here. You could have made something meaningful easily. Like, (1) it would make the rocks fall in front of the player and not behind him, so it would be an obstacle (he would have to jump) or (2) the exit could be on the top of the lvl and once you hit the switch you have to go back and jump on the rocks to get through the exit.
see what I mean? The idea of the first lvl is good, but not meaningful for me.
Second lvl is really nice and intuitive. Good work here.
Third lvl: Once again I'm not sure of that mechanic of "You have to go back to your soul before you die." it's frustrating and not adding so much to the game. Specially since it's slow on my computer.
4th lvl was really good. But once again.. That thing with the spikes.. grr.
I really like the 5th lvl, but once again the "your soul can go through spikes" is not intuitive.
Actually I feel like you should interchange Lvl 5 and lvl 6. In the lvl 6, you can "see" that your soul will get through spikes. Because of the moving platform. It's just intuitive. And then in lvl 5, if you know that already it'll be okay.
Talking about lvl 6: I love it! Good use of the checkpoint in this one.
Lvl 7 : Good one, but, I had issue for the moment where there's the checkpoint. It's difficult and it doesnt have to be. I think you should add some space on the right. Like one cube or something.
And I didn't get why you put the thing with the fire bullets (except introducing the bullet of fire, but it feels forced actually). Feels useless. Could be nice but something is missing to make it meaningful I think
Lvl 8: This one has problems. Figuring how to solve it was hard and not so fun (but it could still be nice though, sometime puzzle game does this.), and the checkpoint feels bad. it feels like "oh here's the last danger so incase you die you would respaw okay?"
Lvl 9 : What a pain. I broke the game here, trying to solve the puzzle (attached a screenshot.). The puzzle felt "difficult because it's not clear" more than "difficult because I'm stupid" ; but I can't tell, didnt finish it because of the crash.
You should add a lvl select at the begining, because if I want to get back to the lvl 9 and 10 and give you feedbacks, I have to do the whole game again and I don't feel like doing it.
So, this was a cool game, it's alpha and there's still things to improve here, it's normal. I tried to give the more feedbacks and advices I could. But you're in a good way What kind of game will it be? Like, a free play in browser game, or a full game that you plan to greenlight (If you work hard and make it really really good it could be a thing I think.)? You have any idea?