Revealing mistake: A lot of the CGI was quite good and, even if not totally realistic, was interesting and exciting to watch. However, the man supposedly rappelling (or abseiling) down the mountainside was obviously not there - his feet didn't touch the mountain. (00:36:10)
Revealing mistake: After most of the people trying to hang onto other people holding onto the ascending helicopter fell off, a downward view from the helicopter showed a man effortlessly hanging onto the landing skid and a woman just as effortlessly grasping his jacket's shoulder. (00:02:50)
Revealing mistake: Obvious use of green screen for buildings across the street. On and off, the background fades, and buildings appear higher or lower depending on the camera's angle. At one point, the angle of walls behind Rex (Bruce Willis) is at a downward angle, and his head is almost touching the ceiling. (00:06:10 - 00:07:25)