The cases aren't too daunting, in my opinion - of course, you get frustrated every once in a while when you're first learning them, it feels impossible, you get fed up. It's all very natural.

But eventually, they'll start clicking. Trust me. And it does require some knowledge of basic grammatical concepts to begin with ... and if you don't have a basic understanding of grammar to begin with, by the time you learn cases you'll have a firm conceptual grasp of grammar.

Don't get disheartened! Don't give up. There is nothing unlearnable.

What I find helped me make leaps and bounds with cases - and it's not too hard - is going through texts (whether you understand them or not makes ABSOLUTELY no difference) and just highlight, word for word, the case endings, and determine what they are and what relation they bear to the words around them. After doing this a few times you'll begin to recognize certain case endings automatically, until finally, voila, you'll have a good grasp of the cases, and you'll maybe have learned something else about Russian in the process.