Bug: When you get to the first downed life pod on the second level, if you park the warthog right at the top of the hill and get in the turret, when you look at the big structure, the landscape will change to a snow-covered hill that is a landscape from another level.
Bug: On the map "Danger Canyon" it is possible to go through the stone wall behind the base and pop up on the enemy base. If friendly fire is off, then you can have someone ram you with a vehicle at high speed while you're standing against the wall. Or you can get in a Ghost and drive sideways towards the wall, if you hop off of the Ghost at the right time, then you should end up partially inside the wall, if you jump a few times into the "nothingness" then you may pop up on the enemy base! Or fall to your doom.
Continuity mistake: While playing on any level in Campaign mode, you may have one gun equipped, but a cut scene will always start with you holding an assault rifle.