Of all movies that you gotta watch more than once to really understand, what is your favorite and why?

Not much. Nolan’s films are extremely well made, but about as deep as a puddle. What you see is what you get. If you have been paying attention at the start, at the end you can put together the complete puzzle.

And that’s not meant as a dis, it’s extremely difficult to make a film like that. It’s easy to give the audience too much info or too little. But Nolan mostly gets it right.

Also, he tends to give you the answer in the first scene.

Edit: my pet theory for the different perspectives on Nolan films is that a lot of people just don’t retain information for which they don’t have context. So the first time around, they see the stuff that’s out of place, and that requires an explanation, and they just shrug it off. Then, after the reveal, they remember there was stuff that didn’t make sense, but don’t remember exactly what, so they need at least one watch to make sense of it.

On the other hand, others (mostly people trained by watching and reading tons of SF, to be honest) mentally put these observations in a “spare pieces” box and start actively fitting them to their current understanding of the plot. When they get the final piece of the puzzle, everything makes sense.

The trick is to watch it backwards

I caught new stuff on the 4th viewing. It changed my answer to a pivotal question.