Sorry arsaib, but since studies have begun i haven't checked a lot of the threads on our board...
I haven't seen anything else besides "Summer in Berlin" and The Policewoman" by Dresen yet, but from what I've heard, Nachtgestalten is very good, and most fans of his work consider it to be one of his best films. It may seem a bit rash, but after having seen two of his films and some parts of his Berlinale winner Halbe Treppe (2002) - which made me believe that this might be one of the best films of the new decade, though i still haven't seen it in its entirety - I would say any film by Dresen is probably worth watching.

Don't know if you want some specific info on Nachtgestalten - are you planning to purchase it?