Alright, here we go. To start off, Alien: Isolation is a /good/ video game based off of a movie. We don't get a lot of those aside from Spiderman 2 and the LEGO games. It keeps the suspense that was present in the movie alive in the game and a lot of people agree that it "does scray right". It is also good to vote with your wallet. Remember Aliens: Colonial Marines? Buying Alien: Isolation will help to drive home the message that gamers won't take rushed shovelware licensed games. Just in case you don't remember Aliens: Colonial Marines, here's a link that sums it up pretty well:
http://www.videogamer.com/videos/aliens_colonial_marines_what_the_hell_happened_to_aliens_colonial_marines_2.html

You might be thinking: "Romeo, shouldn't I buy Shadow of Mordor then? To support a game made from a movie that is good? Also, Shadow of Mordor is a LoTR game, and I want more of those!"
Even though Shadow of Mordor does look gorgeous (/r/pcmasterrace approved graphics), it plays like shit. Not performance-wise, but gameplay-wise. It's 17 minutes long, but this video shows it beautifuly. Heads up, the guy comes across as a bit of a douche, but he's right.
https://www.youtube.com/watch?v=6AV9W2ZdmjU

That's why I think that Alien: Isolation is a better buy. It's doing correctly what the last Alien(s) game did wrong, and it doesn't have shitty combat.