Thanks!

I have also tasted cake before, but, alas, it was not the cake that I was promised by glaDOS. 

No, unbeliever, the Cake is True, for I have tasted It! And though the cube may be gone from this gray world, he will live again with the Cake forver.

This is a cute illustration and I like the difference from Portal's visual style. This looks like it could be a page from a kids' coloring book, scrawled over with crayon (a crayon made of pixels).

I think it looked better without the random shading patterns. I think this pallete works best for dark backgrounds, and I think a dark background would have worked much better for your piece.

 I like the overshaded version so much better. 

I wanted to go over the top with the shading so that it was different from the original Portal games.  On my monitor, the colors look fine, but that may just be me.  I tried adding those effects to the portals, but couldn't get them right.  Maybe after the contest I'll make an edit of this.

The lineart is pretty good but the shading is overdone in my opinion.  I would actually go for a more portal styled kind of shading, the shading you did right now would fit better in an underwater scene. The portals should also have a fire like effect and show an image through the portal (Like a mirror) The portals look a bit flat also.  You should also change the backround color, its kind of eye burning. The lineart is still good its just the coloring the needs more work.

Updated! 

How so?  The AA is kinda crappy, but it's pretty difficult with the pallete.   I can't really add any more shading, either.

Portal, one lovely game... u could improve it alot dude.