While the movie
could have spent its entire running time explaining the vagaries of time travel and making sure it had absolutely no paradoxes, in the end it was a story about the ways in which our choices shape who we are.
It was by no means perfect, but I appreciate that their effort was to make a character piece rather than an action film with sci-fi window dressing. I agree that the first half was stronger than the second half. It was fun trying to stay one step ahead of the story. None of it was too surprising. I had a feeling young Joe would end up "breaking the loop" the way he did.
One thing I appreciated was how you could alternately be afraid of and feel sorry for Cid. Here was a kid too smart, perceptive, and powerful for his own good, unable to control his excesses (like most kids) and who has seen and done things no child should be burdened with. The movie really hinges on how well you empathize with Cid. I initially found myself understanding old Joe's motivation. One man ruling the future in such a way just doesn't sound like a good thing, especially since Joe implied the Rainmaker killed a lot of people to get to where he was. I wasn't a big fan of him having to kill children to save the future, but that sort of thing is part and parcel of this type of story: you have to make sacrifices in the present to save the future, and if you had the chance to kill Hitler as a child, wouldn't you?
But then we got to know more about Cid and Sarah, and Joe gradually warmed up to him, and it became clear that Cid was no inhuman monster, just a frightened little boy who could learn to control his power, given the right upbringing. I got a sense of dire responsibility from Sarah very early on, like there was more to her relationship with Cid than simply a mother caring for her son. When I saw her exhibit TK abilities, I realized that Cid's tantrum wasn't just a subjective portrayal from Sarah's POV, but Cid actually using his abilities and scaring the shit out of her (with good reason.) I found that a pretty clever trick by the director.

After that point,
why she felt such an obligation to protect Cid from the outside world made perfect sense. She clearly saw it as a very corrupt and petty place, a place she knew only too well, and she no doubt feared the corrupting effects it would've had on her son--and what damage he could do with his abilities, given no moral compass and no sense of family.
I originally thought it would have been nice to see the future Rainmaker and how he might have been changed with his life being
saved by a Looper, rather than his mother being killed by one. But in retrospect, it makes more sense that we don't get to see it. Young Joe makes what he sees as the only right choice, but he'll never get to see the results of it--nor should we. You just have to trust that things will turn out better. Maybe they will, maybe they won't.
I feel like the people focusing on how the sci-fi elements work are really missing the forest for the trees. It's not
about that. It's just like old Joe said--"It doesn't matter." After all, he wasn't driven by some desire to create a better future in the abstract, he was motivated by love, and the will to get his life back.
Old Joe couldn't think of any other way to secure his future than by killing people in the past. That's who he was. That's how he grew up--as a killer. Young Joe, in seeing this, realized that wasn't what
he wanted. Old Joe was incapable of changing his path. Young Joe hadn't yet lost himself, and made a different choice.
In storytelling terms, it's all quite simplistic and easy to follow from A to B. In character terms, there is quite a bit going on here--certainly more than you'd find in your typical sci-fi thriller.
I'll rank it
Above Average.