perhaps the background (especially in the 1st screenshot) shouldnt have as much contrast to distinguish depth

seconding that. You have your oranges crying for some anti-alias on their edges on 2nd screenshot, too.
I think flies don't fly with their legs extended, too. That would help to hide them for collision guess by the player, too.

Imho, a dark line between the bricks and the spikes on the 1st screenshot would make the scene more comfortable to look at. Possibly it would be good to have more contrast on the candy things. All your colours are very close value-wise.

--
^ BW conversion, will help you seeing whether the scene is readable. -- ways to improve readabiliy ^

Now, to be honest, the background tiles could use some work. They're very irregular, with excessive dithering. The skelettons size compared to the fly might break the illusion that we're a fly.

I suggest you post 1:1 assets in additions to mock ups / screen shots, next time. It will make edits & reviews much easier.

Bilou's School Rush, a homebrew for Nintendo DS you can get good at ...

I don't know if some of you guys played this but fool made very interesting game some time ago with exceptional art as always. My recommendation for enjoyment.   http://www.dojo.com/game/knight-fall

Fun and very well drawn, indeed ... I get flickering issues, unfortunately.

Warning very loud. This was from a very long time ago.

Batman chased by robot bats

Hello, Fassous, and welcome. Good luck with that assets provider activity

Artistic-wise, there are plenty of nice things (the castle, for instance), but plenty other things could use improvement. My major concern would be the lack of unity in the scale and light source:

- barrels size compared to characters (barrels could be at least as large as your shield)
- doors size compared to characters
- right-lit stone (grave?) vs. left-lit tree (with exaggerated highlights for such a distant foliage).
- front-view castle vs. 3/4 view on the other building (farm?)

You could have a more interesting castle if you broke from that square-ish silouhetto. You gave it a nice texture, but little to define its overall shape.

There's something imho quite wrong with your bird. I cannot name it yet, but I think its shape isn't properly defined, and that the colors you picked merge together into a single blob with an outline.  Have you used a reference, for that one ?

50% of the books done, now... I hope you do not mind the bump.