Alien pretty much redefined the genre and set a bar that was not surpassed even today. So yeah, it's easily one of the best movies ever made and the best movie Scott directed. Blade Runner is also an amazing movie, and I adore Thelma & Louise as well... hell I like pretty much everything from him. He is one of my all-time favorite directors, right there with Hitchcock, Kubrick and a very select few.
Vote the Mayor for Mayor!