A story doing nothing but treading water. A loop in which nothing has happened by the end. As with all such stories (alternative universe stories being the worst offenders) it is the equivalent of 'I woke up and it was all a dream'! There can be no tension, no drama, because the viewer knows it did not really happen and putting things back on track will solve every single dilemma that is set up. People can die, come back to life, never have been born but none of it matters because it is all rubbed out at the end with the return to real time or the real universe. So who can care about the story when watching it? Not me. You might argue that Donna sacrificing herself is where the drama lies, but she is alive again in the proper time-line so it is only a manufactured "big deal". But it was produced nicely and could have been worth making if the writer had been forced to live with the consequences of what he did and been able (big 'if' perhaps) to come up with real solutions rather than the get-out 'it didn't happen'.
Review of Turn Left
