The main character is a bit wooden, because he is a stranger in the world he lives in. As a foreigner his German is very bad, and he doesn't really know how to behave in the new environment. I think the actor did a perfect job in this regard. 
I also like the way Fassbinder plays with colors in this film - very reminiscent of Douglas Sirk. 
Fass binder also acted from time to time, and his cameo is nothing unusual. Too bad he didn't act more regularly.