Personally love them. Not so much in German, but in Russian they make word order wonderfully flexible. You can just blurt stuff out, adjusting the case as you go along, to build a sentence, rather than having to go back and restart.

What bugs me with German inability to reliably form plurals and having adjective endings vary by determiner (though not difficult to learn, but just seemingly serving no useful purpose).

For me I found aspect in Russia the most difficult thing grammatically to grasp. I hear learning articles from an "articleless" language is similarly difficult.

My biggest gripe with german is the redundancy, all articles and form changes they create are actually redundant, they don't contribute to the meaning in any significant manners. Remove all of them and all the complications, different forms they create, you would still perfectly understand it.

Yeah I know, languages, organic, beautiful, but subtle things , etc etc.. But still.

I quite like the cases, personally. If you're not in a more formal context or writing (like say you're talking to friends or so) it lets you be a bit more fast and loose with word order, plus it can let you say things more concisely than you can with english. The only real solid annoyances I've had were adjectives. Learning all of the rules and endings around them sucked on some level and it felt really quite superfluous, but once you get them and you can gauge correctness just based on it "sounding right" it's not so bad.