Safety Not Guranteed

Writes Roger Ebert: Few descriptions of "Safety Not Guaranteed" will do it justice. It's a more ambitious and touching movie than seems possible, given its starting point, which is this classified ad in an alternative newspaper:

WANTED: Someone to go back in time with me. This is not a joke. You'll get paid after we get back. Must bring your own weapons. I have only done this once before. SAFETY NOT GUARANTEED.

That sounds like a set-up for a comedy, maybe like "Hot Tub Time Machine." It is a comedy in many ways, but there's a serious undertow, kindhearted attention to the characters, and a treatment of time travel that (a) takes it seriously, and (b) sidesteps all of the well-known paradoxes by which time travel is impossible.
That's not to say time travel takes place in "Safety Not Guaranteed." Or that it doesn't. A rather brilliant ending is completely satisfying while proving nothing. What it means is that the story takes place entirely at this time, and time travel provides the subject and not the gimmick.
More here.