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.
Continuity mistake: Regarding Lt. Rasczak - in the scene where he is teaching his students, you can see his left arm where it was previously amputated, and how close it is to the elbow joint. But later in the movie, when he is introduced to Diz, Rico, and Ace in the Roughnecks, you can see that his arm is much longer than where the amputation from the previous scene would have been, even with the "implant" hand that he now has.
Factual error: The last thing Rico's parents say before the meteor strikes is, "Looks like rain," as the sky outside gets darker. As a large meteor (large enough to destroy a major city) makes it's appearance in the atmosphere, there would be a flash of light brighter than the sun. Several minutes later a dark dust cloud would rise, but by then everyone in the vicinity would be killed.
Plot hole: A Bug meteor knocks out the Roger Young's communications. She dodged it at sublight maneuvering speeds, indicating that it is moving fairly slowly. If it is so important that she warn Earth it's coming (which is how we know their comm was damaged), why doesn't she jump back to tell them or destroy it herself? Even if she has no capital ship weapons (she is a troop carrier), there is no indication that her faster jump drive is damaged or needs longer than they have to warn Earth to charge for a jump, or that she can't leave her patrol station, etc.
Continuity mistake: At the scene where they get trapped at the fortress, you can see they are not shooting in the direction of the bugs. (01:31:25)
Revealing mistake: During the last play of the football game, Dizzy throws Rico the ball and he does an impressive flying flip over several players. Right before the flip, it's extremely obvious that Rico runs up an off camera ramp/stairway in order to perform this flip.
Revealing mistake: Just before Dizzy gets skewered by a warrior bug, you can see breakaway panels on her body armor at the points where the CGI bug impales her, to cover the squibs used to make the holes. The shot is already shown in slow-mo so it's easy to spot.
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. (00:59:15)
Continuity mistake: During the defense of Whiskey Outpost, as the Roughnecks fall back into the compound, one trooper is struck in the back by a bug. To his left there is only one trooper on the platform, but as he is hit, two troopers jump down.