Pros:
* The graphical style is clean and easy to read (It's clear what not to touch.)
* Having stars to unlock more content is always a good hook.
* The levels are relatively short, which is a good idea considering the difficulty.

Cons:
* The controls are very spastic, at least on PC with a mouse. (Might feel a little better with touch controls?)
* The difficulty just starts extremely high and doesn't let up, punishing you for the slightest mistake.
* A little too close to Flappy Bird. Maybe add some small twist to it to make it more uniquely your own.

Pros:
* The concept is interesting
* I like games like this that just drop you in and give you time to learn what to do.
* Controls were intuitive enough.
* Graphics were fine and could simply be a low-res style that you can develop. (It probably looks less good to people when seeing the debug text [I assume is debug text] plastered against the background like "You found a secret", etc.)

Cons:
* The controls were a little inconsistent. I was able to double-jump for a short while, and then I couldn't anymore for reasons I could not decipher.
* The effect of zooming back to start for touching a slime is a bit jarring and tough punishment.
* The left side of the starter area is just an invisible barrier. Might want to add something visual so it looks like a barrier.
* I like exploring and learning what things do, but I'm collecting purple coins with no idea why I'm collecting them or what they will be used for.
* Music is a bit repetitive. There's actually a good selection of stuff to find in Creative Commons 0 on Freesound.org. It's worth a look.

Pros:
* Great atmosphere! The graphics & sound work really well together to create a creepy, otherworldly environment!
* Fun concept! Reminds me of a cross between Metroid & Turrican
* Controller support is appreciated! (Played with PC XBox controller)
* Nice touches with the environment like the swinging foliage.

Cons:
* The controls themselves for moving are fine but aiming is tough because the crosshair is snapping to 45 degree increments. It would feel nicer if the reticule could maybe rotate around your character as you aim the stick so you could shoot at angles in-between. (Supporting aiming with the right-stick like a twin-stick shooter might work too.)
* The collisions with enemies and the environment would sometimes send my character flying and the screen scrolling is tightly anchored to the player so the camera tracking can be very jarring sometimes. Maybe add a little bit of an elastic leash to the camera so it wants to follow the user always but has to move to the player's position over time, that way you get smoother scrolling if the character's position changes quite suddenly over a short span of time.

Pros:
* This is a good start for a game in the style of classic vertical shooters. It's still a fun game style to play.
* Controls are pretty good, though a little floaty (it feels like you drift a little) but maybe that's intentional?
* Holding space bar fires continuously is greatly appreciated! (I don't want to accelerate an onset of Carpal Tunnel Syndrome with games where I have to constantly jam on the buttons to fire over and over again.)
* Starts easy and difficulty scales up nicely.
* Some variety in enemy formations is good for mixing up the action and keeping players on their toes.

Cons:
* Despite the different enemy types and movement formations, the action can be a little repetitive. Are you going for something like Geometry Wars where the action just keeps getting more intense without a break? If not, maybe consider putting in a short break with "Wave 1", "Wave 2", etc. to give the player a quick moment to regroup and also feel like they're making progress.
* Will there be power-ups or some other feature that will give the player a little more in terms of strategic options for how they play? That would also help provide a little more variety and less repetition.
* Some additional polish items (small bursts when enemies are defeated, rather than just disappearing), impact FX & sounds when your ship's bullets hit targets, etc. will go a long way to make the moment-to-moment gameplay more satisfying.

What's here is already pretty good, though. Nice work!