For me a bad movie is a movie with low production values, horrible actors, a shitty scenario and so on.
The Hurt Locker had none of that, quite the opposite.
It doesn't always have to be horrible actors. With some movies it's just the opposite. I've seen atleast a couple of movies that had pretty well known actors in a movie, but it still sucked balls.
Prime example: In the Name of the King. (Not to mention most of Uwe Boll's movies are just horrible. He just seems to fuck up every movie they give him.)
As for the Hurt Locker, I quite liked that film.