The main problem in German is for me the gender of nouns. The gender plays a great role for the declension (as well as in Russian). But in Russian one can almost always easily distinguish from ending, what the gender has the given word. In German this is much harder. It is possible only to determine more or less exactly the feminine gender. All the others have to be memorized.
Another problem is the order of words. The German's one is IMHO much more complicated as Russian's. In all other aspects, I think, German is not so hard for learning as Russian.
PS. Sorry for my errors, I just learn English (as well as German)
Das gr