Premise - 16/20 - A simple premise, but eventually a bit misleading. Regardless of that, I like the occasional small cast, no frills thriller, so I'm in.
Cast/characters - 16/20 - Great lead. Good supporting cast. Interesting characters, but not enough time to really develop them; however, their backstories are hinted enough to where we understand motivation.
Story - 18/20 - Dialogue, and then a twist. Dialogue, and then a twist. A little action, and then a twist. I like that strategy, because you never feel comfortable. This is where the premise was misleading, though; it wasn't really a "whodunnit?", but more of a constant "what the hell do I do now?" issue. That made it a great watch with a pleasant ending. The director did a lot with a little.
Dialogue - 13/20 - Very direct dialogue. Hinting at backstories, showing character traits, explaining mindset. All of that made the last half of the movie understandable. The knock, then, is that for a small cast, dialogue is key, and this is really bare bones with great delivery.
World-building - 12/20 - Blizzard, secluded area in the mountains, basically one small room and some external shots. Nothing crazy, but all of it useful to the story.

75/100 - 4/5 stars - I thought it was great. Simple and not extremely original, but it was like a play that simmers through Act I, gives you a new perspective in Act II, and hammers home Act III. I'll recommend this one as a quick and riveting watch.