I feel about Looper the same way I felt about Moon - - it was a competently executed movie with realistic characters and a coherent plot.* Big budget scifi movies like Prometheus have so lowered the bar, that just putting together a movie where the characters don't behave like morons seems like a triumph.
That said, the movie was simply fine. It wasn't particularly stylish. It wasn't funny. It didn't offer any brilliant new designs or costumes. There was no mindbending twist. I didn't care if the protagonist "won." JGL's efforts to look like young Bruce Willis just resulted in a lot of really strange facial expressions. And the movie comes to a screeching halt 3/4 of the way through so Emily Blunt can give a little speech and smoke. I can't even remember what she soliloquized about, but presumably adding the scene was a precondition to her taking the part.
It felt like an assembly of ideas from countless other superior comics and movies and anime. It's fine, and worth a viewing. But that's it.
*Not to say the plot was great. It only worked if you accepted that one character was an unstoppable remorseless murder machine, except when the plot required him not to be.