Items look quite nice because they don't have large single colored surfaces but like Mora pointed out the shading is either missing or too subtle. That's especially visible on the characters. Details and shading are really missing there.
Search for "pixel shading" on the web and you'll find a ton of nice tutorials how to improve your work a lot!
@ Gaios: Makes no sense. One file is gfx stuff, the other would be sound files. It's not the same.
The rule would be broken if you edit the gfx files and upload a second version of it.