Try looking at more indie games: Cave Story, Spelunky, Hero Core, and N all present polished gameplay experiences for the convenient price of free. There's plenty more where those came from, and as you branch into the multi-person studios who have the gall and audacity to charge a nominal fee, you find mid-length games in more and more genres. (I'd point out Aquaria, World of Goo, and Knights of the Chalice.)