Samus is alone on a space station full of X Parasites, a thing that nearly killed her (and later you'll find out some other stuff about them). She had to have her power suit surgically removed from her body, and her appearance was radically changed. When you go aboard the station, you hope to find survivors - in vain, of course. And through it all, the only "friendly" voice you have is a computer which Samus named Adam, after Adam Malkovich, her former CO.
You're alone. You're trapped with things that very definitely want to kill you, and I don't mean like the Metroids that just want to eat and grow. The X want Samus dead, personally.
Sure, it's a colorful GBA game built on the same engine as Wario Land 4. That doesn't take away the horror when some of the plot beats hit.