I love Looper, but it kind of abandons the time travel stuff in the last act. The Bruce Willis meeting himself conversation in the diner is one for the ages though, such a good way of writing off the "well, actually" paradoxes by essentially saying, "we could pick at this all day, but honestly, who gives a shit?"
Primer was great. I was honestly gobsmacked when I watched it, but there wasn't all too much of an enjoyable arc to it.
Timecrimes for me is the winner here. All great time travel fuckery. The loop being so short makes it one of the few examples of a complete time story with very little room for those problematic paradoxes.
