There's a couple thick and slow paced thrillers from the 60-70th that I hold very near and dear to my heart, but that I can't seem to be able to enjoy again. French Connection, Marathon Man, The Conversation, Taxi Driver etc. I've tried to watch them again but stopped because I couldn't get into them, as if I watched it just for an academic purpose instead of just sinking into the plot. Truly sad.
The Conversation is one of the strongest movie memories I have. Don't really know why, it's incredibly slow.