Even for a bad horror, this is a BAD movie.
It contains all the elements that a horror needs. A parasite that takes over people, a former play mate and a lot of hot chicks, a group of young people, "I think we should split up", the parasite that infiltrated the group, end boss, scare moments, a hint towards the "solution".
Clues are too obvious, scary moments aren't, plot holes so big you can park a school bus in them. Everything is wrong. Except maybe the hot chicks and even that is debatable.
But still, this movie is quite entertaining. Don't watch if you want quality horror, but do watch if you want entertaining humorous horror.