ratings:

5- awesome/watchable through times
4- really good/excellent
3- good
2- ok
1- bad

Concentrating on watching the films of these directors (for a basic education and a understanding of their full filmography):
Pedro Almodóvar, Ingmar Bergman, Robert Bresson, Francis Ford Coppola, Howard Hawks, Terrence Malick, Roman Polanski, Michael Mann, Orson Welles, Alexander Sokurov, Fassbinder, Herzog, Luchino Visconti, Fellini, Rossellini, De Sica.

For further interesting directors I want to look into:
Leni Riefenstahl, Carl T. Dreyer, Satyajit Ray, Jaromil Jires, Věra Chytilová, Sergei Parajanov, Alejandro Jodorowsky, Jean Eustache, Mikhail Kalatozov, Youssef Chahine, Pedro Costa, Bahman Ghobadi, Jaques Becker, Kim Ki-duk, Sharunas Bartas, Mikio Naruse and Godfrey Reggio