I'm on the 'movie can only lose me' side, and mentally penalise a film every time something bad or stupid happens (and then add points back if something good or impressive happens which undoes it). So the viewing experience is essentially balancing the scales. I nearly always watch the film all the way through to the end and give it that opportunity to turn itself around (unless it's really, really bad), so often I end up liking a movie because the third act has redeemed the whole. Though often, sometimes the third act might fizzle out an otherwise great or ok movie.

I'm usually less accepting of stupid things, or stuff I feel doesn't make sense, which is probably why I have such an intense loathing for the Transformers movies.

What I do find fascinating is how easy it is to come out of most movies feeling like it's been a great film. You've got that euphoric 'I've just seen a movie' feeling that lasts until you've got back to your car.  You want so badly to have loved that movie and to keep thinking it was the best thing ever. Ghost Protocol was one such movie that I remember most recently where this happened, hugely enjoyable as you're watching it but as you're driving home you begin to see its flaws.

Meh, you don't have to watch them.

*looks around* Did it work?