Zardoz. Seriously! From Jonathan Rosenbaum’s 1985 reappraisal:

Probably John Boorman’s most underrated film—an impossibly ambitious and pretentious but also highly inventive, provocative, and visually striking SF adventure with metaphysical trimmings (1974). Set in a postapocalyptic society in 2293, it stars Sean Connery as a warrior and noble savage with dawning awareness; interestingly enough, the plot in many ways resembles that of Boorman’s best film, Point Blank.

It’s such a strange movie, and it doesn’t quite succeed, but the leap it attempts is admirable. The surreality is the main reason I find it so memorable. It’s definitely not like the other films on the list.

I’ll say it, too: Zardoz. Don’t bother thinking about it, just watch the damn thing. It’s amazing!