Right: but one difference (which you sort of hint at) is that German is consistent in why something takes a particular case compared to Slavic languages (e.g. direction vs location), and at least the preposition is consistent. Is it "nad morze" or "nad morzem"? No way to know without the entire sentence. And "morzem" is the "tool case" -- the form you usually use to describe that something happens with the help of a tool even though the sea (morze) is not at all a tool in that sentence. Oh, and you only use "nad" with bodies of water by the way. Sorry!
Another incredibly tricky one for Slavic languages is imperfective vs perfective aspects. In most other languages, perfect vs imperfect is just a standard construction. In Polish (and Russian, though my examples here are Polish), you change the verb itself. How? Well, sometimes you put "po" in front of it, like rozmawiać / porozmawiać. Sometimes it's "z" (jeść / zjeść), sometimes "u", "na" or "wy". And sometimes you just give up, like oglądać (but obejrzeć in the perfective), widzieć (zobaczyć), mowić (powiedzieć).
(For this reason I have found it very hard to progress in Polish without conversation with native speakers who aren't too polite to correct me.)
Yes, perfective and imperfective aspects are very tricky, particularly how they interact with various other linguistic features: imperatives (and the negative imperative), the subjunctive, and verbs of motion come to mind, each of which modifies the use of the aspects in it's own way.
Another incredibly tricky one for Slavic languages is imperfective vs perfective aspects. In most other languages, perfect vs imperfect is just a standard construction. In Polish (and Russian, though my examples here are Polish), you change the verb itself. How? Well, sometimes you put "po" in front of it, like rozmawiać / porozmawiać. Sometimes it's "z" (jeść / zjeść), sometimes "u", "na" or "wy". And sometimes you just give up, like oglądać (but obejrzeć in the perfective), widzieć (zobaczyć), mowić (powiedzieć).
(For this reason I have found it very hard to progress in Polish without conversation with native speakers who aren't too polite to correct me.)