For an art site, it doesn't have very vibrant colors and nice text. It also, need to be a more creative template inside of something conventional.
I would change the Artopia logo text on the left -- it's very hard to read. Other than, it's pretty nice. P.S. You misspelled "pieces" on the top, xD.
you want the logo of your site to pop so people notice it, also the text in general is small and difficult to read color wise
NL flipnotic? great design ^__^ (though for selling sake i would change the content text style to none rather than smooth, you cant really do that when coding the design unless you want the entire design to be an image. hope youve found someone willing to buy :F )
I like it how you have built the site around the banner and the images that will be previewed on it, well from what I can see. A little thing I see is how you have the top two bars that are rounded, then you have the 3rd to the left side which has square. The top-left interacts with a round border. To me it's really annoying. Other than that, it's a great job.