I recently watched Welcome to the Jungle (The Rundown) staring the Dwayne 'The Rock' Johnson and a film with him just sounds lame. But it was a good film, not just good for the Rock, but a good film! Very surprised by that, and I really enjoyed it. I also watched Big Nothing staring Simon Pegg, and I had never heard of it before and it sounded a bit lame, but again it was a really good film.
By hidden gem I mean films that are hidden from the audience that will enjoy them. The film could be hidden because it was relatively low budget, and had little to no advertising. Or because it's own advertising/promotion/actors/synopsis shrouded what the film truly was. I don't mean simply hidden from main stream.
So what about you? Any surprisingly good hidden films you know of?
EDIT: When posting a film, post it with an IMDB link if at all possible.