Pi(1998), directed by Darren Aronofsky, would be my pick. I hated the movie in my first watch but that was the time when my watchlist was rather slim and I wasn't wise enough to truly grasp the subject matter. After many years of movies experience I gave it a rewatch and I was truly amazed how with such a low budget Aronofsky was able to give an intense, bizarre and somewhat horrifying experience to moviegoers .
The special thing about the movie is really it's bizarreness. A genius' quest to find a pattern in "pi" and hence unlock a code to Wall Street that begins to transform into an adventure that could answer the biggest questions of Human Existence and GOD plus atypical cinematography that revolves around a man sickened of genius are truly the spirit of the movie.