Aliens Colonial Marines (ACM) is a great example of a poorly rated game that is quite enjoyable if purchased after a huge discount and lowered expectations.
The Plasma rifle alone is worth it. Sometimes a gun(s) can make a game, the Desert Eagle in Half-Life: Opposing Force or the M4 and AK in CS:GO, in ACM the Plasma’s unique sound adds to atmosphere.
Rapidly firing the Plasma rifle while running for your life is just great.
I recommend giving this game a try, especially if you love the Aliens movie franchise.