For me, a good ending is the make-or-break element of most movies. I'm OK with nebulous endings, sometimes. But not very often. I'm more OK with those than with the miraculous Problem Solved ending. It seems as though the writers (I think of movies with poor endings as being the work of a committee) said, "Well, we've done everything we needed to do. Got the scene with Nicole Kidman naked. Got the trippy special effect with the electromagnetic pulse. Got the Michael Mann driving scene. OK, let's wrap this up."
Hey, I'm not saying I'd do better, but I'd be OK with fewer, better movies. On the bright side, the prevalance of deus ex machina endings means that a good wikipedia article has been written, or at least one that contains a good for-instance:
(e.g. the rope that binds the hero's hands is luckily chewed off by a rat.)