Rather a lot, including a gruesome decapitation. Lots of battle related scenes and some scenes of menace related to the alien creature.
Red "tentacles" of the Alien shoot through walls, ripping into people, and splattering bits of blood as the people get pulled out of view.
A couple people are stabbed in a fighting scene. Blood is shown when they are stabbed. A man is stabbed in the neck, blood sprays from the wound. It is graphic, and may be disturbing to many. A man's head is chopped off, and blood curls and sprays from where the head used to be.
A girl wakes up in a cave. There are bodies of dead people all around her. Most are missing body parts. It is rather graphic and may be frightening and disturbing for some. A skull, still with flesh on it is seen for a couple of seconds. The head has blood, and it has been clawed through. It is quite graphic, and may also be frightening/disturbing.
Possibly one of the most disturbing parts of the movie is where a man is captured by a smaller alien. The man is seen from a distance laying on dead bodies while the alien rips at his insides. The man moans and groans in pain, clearly not dead. This is seen from a distance, but it is bloody, and arguably one of the most graphic and disturbing parts of the movie.
The alien tries to kill a girl, who kicks it back. It drops saliva and blood from it's teeth on her, but is interrupted. She is then buried under a pile of dead bodies by the alien's tail.