Quite apart from the infamous torture scene, which I found extremely difficult to watch without howling in horror (actually that's a lie, I DID howl) this film is FULL of nervous tension that occasionally boils over - the way it's been done is masterful. The bouncing-ball scene in the darkened building should be utterly prosaic, but it really isn't - the way it's choreographed and shot brings such an air of menace and trepidation you'll be biting your nails off. There's much of a similar vein in 'Marathon Man', and although the storyline is sometimes almost buried through the relentless suffocating tension, it's extremely watchable (with a cushion to hide behind at certain points) and one of the greatest non-Hitchcock thrillers I've ever seen. Don't hesitate!
Review of Marathon Man
