This is my first introduction to these classic movies and it was a stellar beginning. The suspenseful nature of the survival aspect of these movies is emphasized by some varied and truly frightening alien creatures that surprise and excite around every corner. Ripley played by Sigourney Weaver plays a character that is tomboyish, but well suited to take on the Alien hordes.
Both movies take a similar route with a spaceship flying into an unknown atmosphere that promises danger and eventually delivers a chilling environment. The first movie does this more directly, while the second one deals with the aftermath of the first movie and thus starts more slowly. In both movies the crew slowly becomes overridden by the alien infestation and the majority of the crew members seem to die by the end of the films with the exception being Ridley Scott. The atmosphere and building suspense of the movies is excellent and the cheesiness level of the movies is less than some other science fiction movies. The acting and directing is better than the recent movie Prometheus by Ridley Scott, which is also solid in its own right as well. Aliens is far better than the latest ventures of James Cameron like Avatar as well.
These are both great movies for people that want to experience a tense atmosphere with interesting creatures thrown in for good measure. Alien has a slight edge over the sequel because of better earlier portions.