imo, you might want to adjust the contrast of the bgs.  They seem a bit too sharp and that makes it look like it's at the same distance from the viewer as the foreground tiles.  Just imo though :)

its a game.. I dont follow realistic stuff, i use my imagination.

i like the character. looks good, i like the crate as well but it seems a little to big for such a small character...

i also like the tiles you used for the roof of the cave level. the rest of the stuff didn't phase me at all.

 I like the main character and nearly everything except the turtle enemy... Enemy is in a different style - different type of eyes, legs etc. 

wow~ nice mockup~ though i suggest to remove the clouds outline for the top one~ =P

Täähän näyttää tosi hyvältä. :) Ihan oikeelta peliltä ^_^ Ton ekan kuvan tausta on aivan iiihana! <3 I love it!

Vesi vaan näyttää vähän häijylt tos kakkoskuvas. O_o muttei tossa ekassa.. Weird..

I think that's not a waterfall, but just the water. And it's in the first screen as well. 

Bottom screen is my favorite for sure. I really like that lava and those crates. The "groundtiles" are pretty good as well.
But the protagonist/turtles and backgrounds don't look very good, which takes away a lot of the awesomeness for me. 
 

Very good work!

Boby is a monkey? Just kidding! xD

awsome work

Although like other people already suggested, the turtles don't really fit with the style.

Overall it looks really good, a nice bright color set.

Thanks for all the feedback! Wasnt expecting so many comments :p

Very amazing. But those turtles are ugly and don't fit. On second screen there is grass in the air where the tile curves.

Good work otherwise. 5/5

edit: no.. third screen, not second.

Lovely! I like the vibrant colors, and the style is very consistent. I like it. I'm not a fan of the outline of the clouds in the top one. I would go with something lighter, and AAed to the bg color. Even if the clouds move, they are going to be over the same background the whole time right? So AA would work. Just a thought. I love the lava bubbles in the bottom one, by the way. Nicely done.

 Remove the transparency for the first two levels. Also, the gears look like a rotation tool was used for them. Make sure there is no angle for them. The AA on the giant purple things looks like it needs some work. On the third level, the fourth grass patch is not completely touching the ground. On the fifth level, I don't know if this was done on purpose or not, but it looks like there is no end to the smallest metal platform. Maybe add some waves on top of the water, so it doesn't look as static. Maybe AA the clouds a little. Looks great!

Yeah might be, thanks :)

ooo, love them all.  :)  most of all the lava one.

I know it's allready been accepted, but it might be a good idea to get rid of the semi transparency on the waterfalls, second from the top.