Horror, thriller. I don't care. That movie creeped me out. Particularly Alan Arkin.
When they made The Rocketeer a few years ago, Alan Arkin played the older, techie friend of the hero, 'Peevy' Peabody. The guy playing Howard Hughes in that movie found out Alan Arkin was to play some scenes with him and he was a little scared to actually meet him, after seeing him in Wait Until Dark.
When the guy finally met Arkin he was shocked to find out that Arkin felt the same way about him. Hughes was played by Terry O'Quinn, who had played the creepy bad guy in Stepfather and Stepfather II.
They're both good actors.
Scariest movie I ever saw, horror or not, was the original Alien. I saw it at an afternoon showing when it first came out at a theater in San Francisco down near Fisherman's Wharf.
My wife was at a class that evening when I got home. When she got home from her class later she asked "why are all the lights on?" Without thinking about it, I had turned on lights in our apartment that we had never turned on.