Number_34 posted... WTF at 4:19 in the video. The player shoots the explosive barrel and the alien remains standing. Either the aliens in this game are complete bada** or the game needs a little bit more work on the physics engine.
Or it's a bit of humor. I laughed at it. You see a barrel and think oh, so this is what the game designers wanted you to do, but no. It was too obvious anyway.