This film is, while decently suspenseful and tense, a moderately forgettable fair.
There was quite a decent amount of hype when it came out, and to an extent, Green Room delivers. The story is decently enjoyable, there's good gore throughout, and many of the actors did their parts well (especially Stewart). It's not all good, though, as the character of Amber, from my perspective, seemed to be a red herring for most of the film, and it was never really touched on. And near the end, a few scenes fall a bit flat, though the final scene with the dog was extremely well done, and more so, deeply sad.
Green Room's a good thrilling film with good gore, but ultimately, I don't know how memorable it'll be. For what it did right, overall, I think the movie's just about average. Not much more to say on this one.