to be honest they're all pretty cool. Aquaria is an Independent Games Festival winner. Lugaru is sick if you're into awesome fighting rabbits. Penumbra: Overture is highly rated across a bunch of gaming sites including metacritic.

Lugaru is reminiscent (at least to me) of the Redwall books. It has awesome combat and you shouldn't miss it.

Aquaria is an amazing adventure game that is somewhat reminiscent of Metroid in how you explore the environments. The environments are beautiful and the game play is fun.

Penumbra Overture is a horror game that has scared me more than any other horror game I have played. It has an incredible atmosphere and is definitely worth the play through. The game ends on a cliffhanger, but the sequel is even better than the original, so I would recommend getting both.