The layer effect of your main page is very cool. Haven't seen a site like that yet. Thumbs up. A little description on the main page might be nice. It's not apparent what your site is all about unless you click around.
Nice clean design and great AdSense placement. The link unit on the top stands out as an ad to me but might not to the average visitor looking for wallpaper
My instant concern here is you are a HD wallpapers site; but don't have a fluid layout? It's fair to say most of your visitors are going to have widescreen and indeed large monitor resolutions (thus why they are visiting your site!) so why not use the extra white space by making the layout fluid? The site also needs a logo of some form - and one that matches the domain. It might be worth showing off some of the best wallpapers on the homepage with having them as the full width background images? That would be pretty nice and would stand out a little more against the backdrop of thousands of other sites like it. I did get a teddy bear wallpaper from the site though; so thumbs up for that!
Hi agree with TrafficCake. That's a big mistake not to give importance to a logo(Brand). The general design to be honest it's a little "old". I think it must be more modern and friendly user. Thanks