I know it's poor HN etiquette to pile on 'Me too' responses, and I'm ordinarily very good at refraining, but in this particular case, Primer can't be recommended enough.
I've watched it about 8 times now, and I'm only 'mostly' sure that I understand all of it. It's brilliant beginning to end, and is sometimes on Netflix.
Wonderful movie, the script is smart and complex, budget is tiny, ideas are huge. Watched it 5 times, still don't get parts of it, but it's brilliant.