Critique:

You should smooth out the player's jump arc as well as the moving platform's direction reversal... right now the jumping motion doesn't really have an arc, it's just up and then immediately down. It's hard to judge when you're approaching the top of your jump. Additionally, since there isn't any visual indicator of where the platforms are reversing (since they aren't slowing down or hitting against some physical object), it's hard to judge when to jump on/off of them... this resulted in a number of deaths for me.

I don't think having a timer on the crouch is a good idea since you already have a trade-off - the player can't move while inside the shell. Plus, the time you get for the shell instantly resets all the way once you let go of the key, so you can quickly depress and repress the key to keep crouching... it kind of defeats the purpose of limited crouch time and just makes things more complicated - think bunny hopping or "strafe-walking" to move faster in FPS games.

Also, collision was off in a few places... I think the bullets have a larger hitbox than they deserve, and I kept mysteriously dying when trying to jump up to the floating platform hovering above the lower one near the end of the stage - perhaps the crush detection was misfiring?

Otherwise, I think this is pretty good. I'm not sure if it's the horizontal scrolling or the protagonist or what, but this sort of reminds me of Sqrxz.

I'm soooo glad I could make shellmar happy. I was at first griping about a lack of an OST, but then when I realized it didn't need one and it would take away from the sounds and the ambience, I jumped right in.. SOOO hard... I love the checkpoints.. the delivery... the speed of the game... The controls were TUFF but so is being shellmar... I can understand his troubles by playing him in this game.. You really get a glimpse of things when playing it..

I for one was okay with the limited shell form.. afterall, i'd get frustrated sitting around without viewpoint and thinking "what's going on around me?" and look up again.. That's why there was a time limit... not because he couldn't.. because he was paranoid.. and I can understand that.. He's got a lot of crap going his way and all. The writeup was good, the screenshot was nice, the gameplay was more than good, the hue scheme was nice, the checkpoints were almost at the perfect places.. You didn't skimp on them which... helped me a lot.

For being in a river in a canyon you did a pretty good job making this.. Future generations are in your debt.