Top notch movie. A splendid complement to the Alien franchise. Suspense is held quite well through the movie and if you enjoyed the Alien movies, this will do very nicely.
Bad points? A couple - but IMHO so minor they didn't detract from the overall experience.
Despite the intention of the movie to be a different tangent to the main Alien franchise, to me it felt like a prequel, which in this film's case is definitely not a bad thing.