i gave it a second try, and this time it was definitely better. i didn't have the zwiebelrostbraten, though.
I had the "Faschierter Braten mit Kartoffelpüree" ( minced roast with mashed potatoes) and it was quite good ( and it was only €4.20). Mashed potatoes were delicious. But the souce was wery oily again.
The waiter in the end was quite tipsy, which was funny to watch although it was a little hard talking to him, cause he would not understand at the first try.
Anyway, it's a typical old fashioned viennese beisl with a little oily, but good food ( obviously the Zwiebelrostbraten i had last time was a one-off ).