6. Aliens vs. Predator
Most tie-in games like to keep things as tame as possible so as not to tarnish the franchise, but Aliens vs. Predator is the ridiculously bloody exception that proves the rule. In a rare turn of events, the AvP game is considerably more violent than the film series it's based on.
The Predator gameplay is particularly gory, allowing you to rip the head off an unsuspecting marine, spine and trachea still dangling from the bloody mess where his neck used to be.
On top of that, you can even melt a man's face off by spitting on him as an alien. Such gory depictions of violence are certainly a sight for sore eyes.