Nice usability and function. However, if I'm being honest, I think you should look into two things to give the site some polish:

BRANDING AND IDENTITY
In designing an e-commerce site it is critical that visitors understand that people are buying from you and your product is popular. Communicating this from the home page will make visitors more willing to click through and research your product. If your logo and taglines are HTML text it sends the message that you are not invested in the company or you don't have the cash. Neither is very positive when you are trying to get people to buy from you. I suggest creating a graphical masthead/banner across the top instead of the HTML text.

HERO SHOTS OF PRODUCT
I saw your comment regarding the fact that you want the product to stand on its own but at the same time not have a graphically intense site. I think you're half right. A good approach for marketing your product is to make a hero of it by using large shots of it with very little text. You have an opportunity at each main entry point to create sort of an advertisement. Your current design is very utilitarian and assumes visitors will find something. This is a long way of saying that I recommend implementing some kind of "user push" that takes users by the hand and puts the product in front of the noses.

One way to do this is by starting with the home page and selecting three or four main categories of popular products (keeping all lines in your global navigation across the top like you have them already). Spotlight these areas in a more billboard type layout like this example http://www.neimanmarcus.com/. Then emulate this "hero shot" on the main page for all your categories. Selecting items you know people are interested in or extreme discounts.

Just some thoughts for you.