Few thoughts:

- Loading splash is very nice.

- Grid view looks good. Would like to see your take on the "list view," which I generally prefer.

- The chat seems to waste a lot of space, especially with the top bar. The current Steam interface is much more information-dense, which as someone with a 1280x800 screen, I very much enjoy :)

I'd love to see your take on a redesigned storefront and community sections, too. I don't really have any issue with how Steam looks now (just how it functions - the OSX app was broken for so long in so many ways!), but I like the visual refresh you've made!