German is a great language eh?

Sure it is. There are so many crazy rules to learn that it is only beaten by the complete mismatch of language and spelling in English, the ridiculous amount of completely silent extra letters at the end of French words, and the number of inflection rules in Latin. It's so hard that even native speakers can have a hard time using it properly.

Examples?

Refer to a young girl as "Mädchen". That's the diminutive form of "Magd" (maid), but that is generally long forgotten. You can still see it by the "-chen" suffix. Because it is a diminutive, the grammatical gender changes from feminine to neuter. That's just grammatical, no implications about biology, social, cultural gender. And so, if you want to refer to that "Mädchen" in the next sentence, you must use the neuter pronoun "es", not the feminine pronoun "sie". If you use "sie", you are doing it wrong. That error is quite common, even for native speakers, even for professional speakers (like the presenters of the Tagesschau).

Comparing criteria. If the amount is the same, you use "wie": "A hat genau so viele Äpfel wie B". If the amount is less or more, you use "als": "A hat mehr Orangen als B", "B hat weniger Orangen als A". Same as in English: "A has as much apples as B", "A has more oranges than B", "B has less oranges than A". But getting "wie" and "als" right is hard, because of regional differences. Many native speakers can't get their head around using "als" when comparing. They always use "wie", and that error more and more also happens to professional speakers.

Grinding vs. looping. Grinding, reducing the thickness of some material by abrasive tools, ist "schleifen", past tense form "geschliffen". Grindung to cut material, intentionally or not, is "durchschleifen", past tense "durchgeschliffen" (strong inflection). Tie a cable across a rough, spinning wheel, and some sand and water, and the cable will be cut through in no time. The cable is "durchgeschliffen". A loop is "Schleife". Forming a loop, especially when handling electrical signals, e.g. into one device, then out of that device and into the next device in a chain, is "durchschleifen". Same letters and same sound as the grinding process, but a completely different base and a completely different meaning. Past tense is "durchgeschleift" (weak inflection). You can still see the "Schleife" in that word. Professionals started to intentionally use the wrong conjugation "durchgeschliffen" for fun, and many other people picked up that wrong form, not even knowing about the loop. Professional speakers rarely get that one wrong.

Alexander

”When a German gets his hands on an adjective, he declines it, and keeps on declining it until the common sense is all declined out of it. It is as bad as Latin. He says, for instance:”

SINGULAR

Nominative --Mein gutER Freund, my good friend.
Genitives --MeinES GutEN FreundES, of my good friend.
Dative --MeinEM gutEN Freund, to my good friend.
Accusative --MeinEN gutEN Freund, my good friend.

PLURAL

N. --MeinE gutEN FreundE, my good friends. 
G. --MeinER gutEN FreundE, of my good friends. 
D. --MeinEN gutEN FreundEN, to my good friends. 
A. --MeinE gutEN FreundE, my good friends.
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From The Awful German Language by Mark Twain

«The Crux of the Biscuit is the Apostrophe»

For comparison, Czech pronoun "můj" (my):

Case	Masculine animate		Masculine inanimate		Feminine		Neuter
	Singular	Plural	Singular	Plural	Singular	Plural	Singular	Plural
Nominative	můj	mí, moji	můj	mé, moje	má, moje	mé, moje	mé, moje	má, moje
Genitive	mého	mých	mého	mých	mé, mojí	mých	mého	mých
Dative	mému	mým	mému	mým	mé, mojí	mým	mému	mým
Accusative	mého	mé, moje	můj	mé, moje	moji, mou	mé, moje	mé, moje	má, moje
Vocative	můj	mí, moji	můj	mé, moje	má, moje	mé, moje	mé, moje	má, moje
Locative	mém	mých	mém	mých	mé, mojí	mých	mém	mých
Instrumental	mým	mými	mým	mými	mou, mojí	mými	mým	mými

The adjective "dobrý" (good) is quite similar, but there are some adjectives with completely different patterns (in total, there are 3 basic groups of adjectives).

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