The plot incorporates paradoxes which means it is impossible. There is no internal coherence, it all comes from the clock in the theater lobby. What happens before, by that clock, causes whatever happens after, by that clock, regardless of what in-universe year the particular events are taking place in. I downgraded the movie one level for this.
However, if you believe that Joseph Gordon-Levitt has developed enough conscience to exercise judgment upon himself, then the movie worked. (incidentally, there is no love story between Emily Blunt and Gordon-Levitt: The character does what he does because he identifies with the kid whose life is repeating his.) Also, the movie completely depends upon accepting the premise that murder isn't just a conflict with a winner and a loser (and whether you care depends upon how much you like the winner or loser,) but depends upon a deep conviction that murder is wrong
My guess is that this will not be a successful movie in today's climate.