The perspective looks way off. If you follow the legs from closest to back and then do the same for the head and body, it looks like they're been drawn on separate horizon lines...sorta. I dunno, it sorta looks right and wrong at the same time. Probably what Cure said about the legs would help.
Also reminds me more of an ant than a spider, especially the abdominal part.
Also wanted to point out your avatar looks completely like a color reduction (pixel - cheating) than pixel art, if you care about that, if not, ignore previous statement.