I saw the trailers and was left both cold and actively not attracted. i read a couple of 5-star reviews that, basically, said the marketing of the movie was misplaced. So ... I rented the movie. Brilliant! The acting of both leads is first class; and their interplay wonderful - witty, dramatic, dark, light, intense, hopeless and more. And the writing, the script, is as good as you can really get. The story is clever; it is hard to write a story about Time - it really is. The dialogues are crisp and authentic; I cannot remember, off-hand, even one cheesy line - and that in itself is a testament to a professionally committed writer. And the way that the repetition is handled, sort of beginning at the same place but with nuanced differences each time, is masterful. Pay attention! It is precise and surgical and every nuance counts. This movie can be watched more than once for this alone.
If you want to watch a sci-fi movie that is brilliantly clever - in story and dialog - this is most certainly one.