My approach is movies that blow our minds, that are so crazy that they could be horrible, but somehow they seem to work (for us). I tend to lean in my thinking toward movies that keep throwing crazy things at us, and don't really stop.
I haven't completed my top five, but some that I am considering:
The Happiness of the Katakuris
Eraserhead
Brazil
Spirited Away
Tideland
A Page of Madness
The Shining
Life of Pi
A Serious Man
Monty Python and the Holy Grail
The Lego Movie
Cloudy With a Chance of Meatballs
Got it?