You're definitely spot on with the Alien movie breakdowns. The third was quite odd, but I recall seeing the first in a theatre and it plays well on the big screen which seemed to heighten the intensity. Any time a director can get his cast to have the average, normal looking interplay during "down" times, it always solidifies a realism in the flick for me. Regarding Aliens, I didn't get that feel as much and what actually significantly separates it from the first is: