"Aliens" is one of the strongest arguments for practical effects over CGI. Everything you see in that movie is real, using every trick developed over the previous 50 years. I still remember what a pulse-pounding experience it was to see that film on a big screen for the first time.
Interesting - albeit brief - interview with the composer in that documentary. I can see why Cameron dumped his wife - she was as big a jerk as he was/is.