Hicks' clothes change from what he is wearing in cut scenes to what he is wearing in actual game play.
Raider 6-5 is shot down. Another radio call is made to Raider 6-5, but a different person answers.
Captain Cruz continually refers to himself as "Sephora Actual," and later "Sulaco Actual," however this is incorrect for a number of reasons. Commanders are referred to by their unit's designation followed by the numeral 6. The company he is in command of seems to be designated "Rhino," so CPT Cruz should be "Rhino 6." Assuming there is no Navy crew manning the ship and Captain Cruz is the commanding officer of this ship as well as the company, he could conceivably be "Sephora 6." The term "actual" is only used in radio communication to inform the other end that the person speaking is that person, and not a radio operator relaying the message. Captain Cruz would refer to himself as "6 Actual," while his radio operator would refer to himself as "6 Romeo." Since this is the future, it is possible that radio protocol has changed.
The developers of the game used the original construction schematics to meticulously recreate the sets of the movie. However the cryogenic compartment on the Sulaco seen here is half the size of the original, and contains half as many cryopods. (Too few, in fact, for the crew of the ship!) When filming Aliens, only half of this set was actually designed and constructed, and a floor-to-ceiling mirror was used to show the "other half of the room" receding into the distance. The developers didn't account for this camera trick.
The position of the laser sight does not match the position of the red dot.
The mass readings for the Xenomorphs in the smartgun HUD show as too heavy to realistically move.
The fuel lines to the dropship loosen with a turn to the right; it is standard for threads to loosen to the left.
The sheer amount of Xenomorphs are not accounted for by plot events, since each one would have arisen from a parasitized human.