Usually free WordPress themes are not the best. They usually have bad designs and are not even worth the effort of installing. Adventure is a WordPress theme which is well worth considering. It's a minimalistic photography or portfolio theme which is perfect for making your content come first. It's one of those themes where you make your portfolio do the talking, not how amazingly designed your site is. It's compatible with WordPress 3.5 and above, and has a responsive layout which is perfect for mobile and tablet screens.
The theme is only available for a limited time, so get it while it's free!