Veering off topic a bit
In my youth (which is too fat ago now) I remember reading something that said a book labels Sci-Fi was likely to be a Cowboys & Indians in space type space opera but if you wanted something a bit more intellectually challenging you needed to look for the label SF. At the time I found this to be a very good guide which is why I still wince a bit at the term SciFi (we'll say nothing about SyFy).
having said that -
Dark Star should be there, as stated I think it was the first "non-shiny" SF film I'd seen, and it's funnay as well.
And Primer, still makes my brain hurt, still no idea of exactly what happened but is a brilliant example of the principle of taking one "let's assume this is possible" idea and seeing where that leads to. (I like Bob Shaw's exploration of Slow Glass over many stories as a literary example of this.)