I actually liked the third version of the post with three, not because of lightness/darkness, but mostly because the other two (and subsequent updates) have had some dither that bothers me. The lighter areas of the platforms have a scattering of pixels that looks sort of like diffusion dither more than the orderly stuff in the darker areas and it just looks a bit messy with the two different approaches, IMHO. But I love the overall look of this. The main character is totally relaxed in the idle pose and that expression (or lack thereof) is priceless. <3

*oops* 

I really like the first image in the thread as a sketch, but the rest don't really do it for me. Part of it is that I like the original palette more, but that one is a bit contrast-lacking, seeing it next to the other one. The others lost some of the personality with the design change and also look really unfinished and sketchy, but AFAIK aren't just sketches. If they are and you're going to refine it at some point in the future already, ignore the rest of this post. But otherwise, I think the issue is that you have a lot of horizontal lines at the ends of things and areas where you have some 2px jumps. Basically it looks like the whole thing was made with a 2px brush. Adding some more 1-pixel wide lines in some places (especially the tentacles) would make it look a lot smoother. Also look at Arachne's edit for a great example of how to make transitions between areas of light and dark less jaggy.

This looks suspiciously like a color reduction or photoshopped piece. The shadow has a huge number of colors and the "pixelled" part has 91. Even if you did this by hand, it needs work, especially in color conservation. If one pastes one image over the other, the outline of the shrimp deviates in only a few areas and several of the details are identical in shape. If you didn't reduce the image's colors, you traced over the outlines, a practice not smiled upon. You gain no skill from putting pixels right where they already are, and it won't get you very far in this community. Additionally, don't use tools to draw shadows or anything else.

I think the best thing to do in your position would be to redeem your reputation with some pure-pixel works or a progress animation that shows how you made this, using pixel-perfect tools (pencil, fill bucket, line tool, no auto antialiasing or gradients). Hopefully this is all a misunderstanding.

...the last 2 semesters of the year? I'm confused.