Mockup Feedback

[fereal]

Hi All. This is my first post seeking critique on this forum. I'm looking to really improve my pixeling skills, and I think sharing my work for constructive feedback is one way to do so.
Here is a game mockup I worked on over a month ago.
I like to let things marinate for a while, before I look back at them to see how I can improve on the ideas I was working on.
What improvements can I make to this?

[RemboRage]

I really like the atmosphere. I guess there is anything on point besides the characters skin colour. If you would make it a shade lighter it would better contrast with the background. furthermore it would be a better contrast to the enemies because the players and the enemies skin colour looks similiar.
everything beyond that is a matter of taste, if you ask me. 

[eishiya]

The contrast in the background is greater than the contrast just about anywhere else in the image, making everything rather hard to read. I think you should start by making the background have lower contrast, and then seeing what else is difficult to read. Your characters look like they'd probably read best on a dark background, so perhaps darkening the sky is the way to go.

[fereal]

Thanks so much for all the feedback! I really appreciate it. Here is an edit with what I've learned.

How else can the color be improved?
How about the UI?
Also, is the 'camera' a little low or just right?
The idea for this mockup is an action platformer type with puzzles and combat. How can I best communicate that?

[Vinik]

This is much better, but I think your mockup would benefit a lot from a more unified, connected palette. I like your shapes, rendering and the scale of objects, but the way you varied the colors from one piece to another makes me feel like you haven't tried to use the colors to give a specific mood to your game, which would be interesting if you want to improve it. However, I like the fact that you made closer objects more saturated, I just think that the shadows are varying their hues in too many different directions without reason. Was reserving outlines only to active/moving sprites a councious decision? You have many different outlining rules in the same piece, I didn't  liked it so much, but that is just personal preference, it is a perfectly valid way to do it.