I still like this movie, but the more I think about it, the problems with it become more glaring. One thing is the whole scenario with Paul Dano's character. Okay, so, they killed the future version of him so they wouldn't screw up the timeline, but they also cut the present day version of him up into pieces. If you're missing your nose, your fingers and your FEET, that's going to affect pretty much every aspect of your future. So even if he survived all that, they still changed the future. And if they did indeed kill the younger version of him, then why go through the trouble of luring the future version back? Just kill the young guy, and the problem is solved.
I also don't think the ending quite adds up. We are led to believe that the Rainmaker was sending loopers back to die because Old Joe killed his mother. But the Old Joe who was sent back in time had killed his old self in the original timeline, as we witnessed, and had never even met Emily Blunt's character. And thus if that happened, then the Rainmaker never would have come to power. Yet somehow he had, and sent Joe back to die. So perhaps an Old Joe from a third timeline had been sent back, or another looper had killed Emily Blunt (because of that whole physics theory about how things eventually come back to the same place even if we deviate from the original path) but this was never fleshed out and Johnson himself doesn't seem to be able to explain it in the interviews I read.
Anyway, like I said, I still really liked the movie, but I think he got too hooked on "getting time travel out of the way" and didn't fully think through some of the "rules," so to speak.