Other mistake: Just after Rico and Ace rescue Carmen, the other guy has hold of the nuke, which explodes. Watch when the rocks collapse behind the three characters, you can see a nice square block lower from the ceiling, almost like a door being lowered. The crew could perhaps have made it look a little more realistic.
Other mistake: During the live fire assault training, Pvt. Breckenridge has trouble with his helmet, and Squad Leader Rico removes the helmet to inspect it. A third private stumbles and falls nearby, and as she hits the ground her weapon discharges once. The camera immediately cuts to another angle, and the woman is still falling, hitting the ground again. Her weapon discharges several automatic rounds this time, swinging wildly from left to right. She is thus firing from ground level, pointing up at Breckenridge and Rico, who are kneeling only about 8 feet away. The automatic gunfire at that range should have struck both Rico and Breckenridge. As an aside, Breckenridge is shot in the head, and Rico is consequently disciplined for allowing Breckenridge to remove his helmet and getting him killed. However, Breckenridge was shot from below, in his right eye, blowing off the top of his head on the left side. Even if he was wearing it, the helmet would never have saved Breckenridge from a gunshot to his eye.
Other mistake: When escaping from the Roger Young, Carmen manages to pilot the escape pod through a debris field, re-enter the atmosphere, bounce off an outcrop of rock, through a rock wall, and bounce off another wall,all without wearing a seatbelt and managing to stay seated.
Other mistake: When the large dropships are releasing the smaller craft with the ground troops on board, the large ships are in orbit around planet B, but there seem to be two different types of physics at play - when the small ships are released, instead of using thrusters to push away from the large ship and begin descent into the atmosphere they are already using thrusters to slow the speed of the descent, even though they are still in orbit.