Portal of Doom: Undead Rising is a great sci-fi horror game that is also very hard. You've got a call for help from the space station, which is where experiments are done. You don't know what happened. Maybe the experiments didn't go as planned.
You have to face your fears and look around the space station to figure out what's going on. You have a lot of high-tech weapons at your disposal that you can use to kill any enemy you find. Look for clues, stay alert, and see if you can figure out what the Portal of Doom is all about!
Have fun and good luck!