Mars has a very thin atmosphere, no magnetic field and its daily temperatures are well below zero. Unless the planet was changed using technologies not shown in the film, there's no way that the characters would have been able to walk around without spacesuits and breathable oxygen.
During the battle when the survivors are waiting for the train to arrive the first time, a sword makes the noise of hitting metal when colliding with a gun, but it bends significantly and is obviously made of rubber.
The goof item below may give away important plot points.
Lieutenant Ballard says that blowing up the nuclear power plant will cause an explosion with a blast radius of up to two miles. However, in the very wide shot of the explosion, the visible curvature of Mars suggests that the resulting blast radius is no less than several hundred miles wide.
the police are very slow to accept that Desolation Williams did not do the earlier murders, even though they were just like what has happened while he was locked up. These are supposed to be a Captain and a Lieutenant, plus a man good with locks.