I started learning mandarin Chinese in 2008 and that was one of the best decisions I've ever taken in my life.
Chinese is a completely different language from English and all the other European languages so it is indeed a challenge to master it.
But people, I did it so you can do it too, all you need is time and patience and practice.
Now back to my original question, is studying Chinese really that hard?
Well it depends what level you want to reach. If you want to be like a cultured native speaker, yes it is that hard but if you want to be almost as good as the average native speaker, I'd say no it is not that hard but it surely isn't easy.
So what makes mandarin hard for many people to learn?
The tones. Mandarin Chinese got 4+1 (so 5) tones and those are really hard to master for so many people because in our language we don't have such a thing.
The characters. To be able to have a good level you need to memorize at least 3000 characters and yes they are all different and some look so similar that is difficult to say which one is which.
Idioms. There are thousands of them. Chinese people do use a lot of idioms when they talk. For us the use of idioms might sound antiquated but for Chinese people is their way to sound more articulate and to say a concept with just few characters but hey don't worry most people only use about a hundred of those and they rarely use them when talking to foreigners.
But hey dude those three things sounds pretty hard and you just said that is not that hard to learn Chinese, WTF???
Calm down dude. So no need to worry about number 3, the other two are difficult but I'd say that's it. Grammar is way easier than grammar in European languages and once you got the tones, pronunciation is not that hard either.
People, mandarin is definitely a hard language but it's really not that impossible to learn. Just go for it.