Rohan15: Ginger Snaps. The Canadian horror movie did an excellent job on portraying lycanthropy as the menstrual cycle for the lead characters. That, and the effects were so cheesy it was good. Oh, and I have a thing for Goth girls.
I remember catching that on late night channel4. It had already started, and i'd just got back from clubbing in london with my girlfriend, and we were kind of drunk, but sobering up due to the endless nightbus ride home. We started watching it cos it looked terrible, then ended up both staying up to 5am to see the end. Was indeed much better than expected.
I totally agree on the Bourne Trilogy and Tank Girl too!
For me:
The Matrix. The trailerr looked like a terrible, low budget action movie. Lots of people in leather and sunglasses jumping about. Was surprisedd how much better it was in full.
Watchmen. It came out much later here (japan) than the US, so by then I'd heard a lot of people bitch about it, and seen poor reviews. And I was a big fan of the comic. But it was probably the first film this year that i really enjoyed.
Other than that, it's usually that i'm too hyped and get disappointed.