How do you judge a movie?

Do you judge a movie, based on the reviews given by others? Or do you judge a movie based on your own opinion? If you are going to say "your own opinion", can you really watch a movie, that's known for it's stupid plot and such? If you are going to say "based on others reviews", why do you consider others opinions when you are about to do something for yourself?

As for me, I would say a bit of both. I do read reviews and if they are mediocre, I am gonna watch that movie and then judge it. Otherwise, I wouldn't even give it a chance.
What about you guys?