Wow! Three other languages. I don't read anything but German and English. (Apart from a little Dutch, I mean. But that's just because it's related enough to German to be halfway understandable when reading it. Don't understand a word when they're talking)

I guess German's hard to learn because it's pretty grammar heavy. I don't know what other languages you read, but romance languages don't decline nouns, which German and most slavic languages do. That's a stumbling block for a lot of learners in my experience.