The front sight of the ISA's main rifle isn't visible when aiming.
When Templar and company speed away in stolen Helghast Attack Boats, they are chased by guided missiles fired at them from a Helghast soldier with a 3-barreled launcher. This is impossible, because everywhere else in Killzone this launcher is found as RPG - a weapon whose rounds have no guidance. This weapon is not, in fact, found anywhere else in Killzone.
Numerous spelling mistakes in subtitles.
All NPCs spawn about one foot above the ground.
Enemies visibly spawn in the Player's field of view (something typically avoided in video game development).
During one cutscene, a Helghast soldier tells the Helghast General that they are approaching a missile base. The subtitles, however, state that it is a transport base.
An enemy will shout out tactical information to his teammates even if he is on his own.
Whenever the Player switches weapons, the action of the weapon that he switches to is cycled - which in real life would waste one round.
No matter what the 'ammunition' indicator says on the laser designator, other graphics list the power as 64%.
The Earth fleet comes from the direction of the planet. It should be coming from outer space.