This film is flawed. It doesn't give enough backstory (forwardstory?) to half the cast. But, it asks all the right questions about the paradox of time travel, while managing to get me interested in the two main protagonists enough that I want to know what else they get up to in a sequel set in the past/future.
If you're unsure whether to watch this, read the one star reviews on Google. Then ask yourself, "Does this person sound less intelligent than me, more intelligent than me, or about the same?" Base your decision to watch or not watch using this information, and you will find it time well spent.