For sheer replay value, Aliens and the Matrix do it for me. For most overwhelming experience watching a film, Irreversible wins hands down for its confrontational content. My poor g/f had to leave after 20 mins of it, it shook her up so much. As far as best movie in the world ever.........Close Encounters of the Third Kind is impossible to beat. It still sends tingly shivers down my spine every time i watch it.
I'd just like to say that it's pretty hard to state one film! Cos there are some class films out there. Heres a few of my faves: Fight Club Matrix Pulp Fiction Shawshank Redemption Swordfish Heat Identity Fantastic -A-
right! fight club full metal jacket lock stock & 2 smoking barrels life of bryan! the holy grail (holy hand grenade! ) trainspotting and belville randevue (if its spelt right)