This Is England
Watched it for the first time today, though I've been wanting to see it since it came out in 2006. I know this film isn't new nor sensationally underground, but it affected me quite a lot.
It's been a long time since a film made my cry so badly. If you get the chance to watch it, do so. But I'd reccommend you to learn a bit about Thatcher, The Falklands War and England in that period before watching. It puts everything into perspective.