Thought this was missing some context, then I checked out your site, and this seems pretty rad.
But in terms of traditional pixel art there's some major issues. The mixed resolution can be jarring, ideally everything would be hand pixeled in the same res, for the sake of consistency.
Secondly, the gradient overlays and laser beam effects are considered not pixel art, for the same reason as above, but I understand its application in this collage type context. It depends what you're going for, true pixel art, or a hodge podge of resolutions/materials that imitates pixel art but isn't true to its core forms.
As for the shark himself, you have some strange pixel clusters and a lot of jaggies, not to mention inconsistent AA. I like the colors but your application of some of them, like the transitional grey between blue and light blue, is not used enough, or should be omitted completely. Also I really like the concept of a hammerhead floating threw space with laser beam eyes, so do it justice! Read up on some pixel tuts or get familiar with the lingo, hope this helps.
