It wasn't the mixing of elements--my complaints stem from the approach and technical aspects. The script needed a bit more polish--the two opening acts went forth at full locomotive speed and ran out of steam once it reached the end of the line.
To me, the third act felt fabricated as opposed to organic segue. The themes and concepts presented are not common in mainstream science fiction, but Johnson didn't really go anywhere with them. Ultimately, he chose the easy way out. The mainstream exit.
Nonetheless, I can understand how Looper is critically lauded.
Upon closer inspection, it is, indeed, a very good movie.
But it should have been great. An instant classic.