Can someone explain to me why I used to get a lot of traffic and now if you google "nature wallpaper" or "Free Wallpaper" I am no where in sight... what is wrong w/ my site??
The site looks very appealing, it's nice and clean and easy to navigate, the content and the ad placement is great. Google has been doing some strange thing with the serp maybe that's why you rankings changed, there is also a possibility that your site was penalized for doing something wrong.
Tons of sites looking to rank for those very same terms, maybe your competition has stepped up their game.
There's nothing wrong with the site. Perhaps your competitors have more backlinks, higher quality links? Do you promote the site? Writing article etc. It may be worth it to try and bump up your serps.