They say that Chinese is a rather hard language to learn, if you're a native speaker of an Indo-European language, e.g. English. I've recently had first-hand experience on learning elementary Chinese, and given my previous academic training as a linguist, I have a few observations.
I think it really depends on the various aspects of the language, and while some aspects are rather easy, others are definitely difficult. Let's start with the phonology. For some reason, this language decided that it is a good idea to restrict morphemes into single syllables. This means that for the language to make meaningful differences, these signals of differences have to be placed somewhere else, not on morpheme length. And on top of that, there is also the restriction on syllable form: there are plenty of various consonants that can occur at the syllable-initial position, but for some reason, the syllable can only end in either a vowel, or a nasal sound. This further removes another dimension where a difference can be made, and therefore the language resorts to other methods of diversification, e.g. the use of so many consonants that are perhaps to the Indo-European ear, are so close to each other. Consonants are not really differed via voicing, but rather via aspiration, and there is a very crowded space, with so many affricates and fricatives. And of course, there are four tones. This rather imbalanced morphosyllabic form is rather difficult to master, I have to say.
Moving into morphosyntax, this is where I think things are rather easy. Combinatorial properties of morphemes are rather straightforward, and the syntax is rather strictly SVO order. The subject always comes first, and actually, unlike Indo-European, elements don't quite move around. I also did not see any evidence for a special "2nd position", unlike in German, where some verbal (or modal verbal) element has to occupy the second position in a sentence, resulting in verbs that have separated elements in the sentence. Also, unlike in English, WH questions are located in-situ: they are not fronted at all. So as long as one sticks to SVO as an underlying structure, then Mandarin sentences are straightforward and relatively easy.
I didn't have enough exposure to have an intelligent opinion on the semantics, but I do have a strong hypothesis that homophony is rampant. This is where the writing system helps, as every Chinese character has an inherent meaning, and so even though it might be pronounced the same (with tones and everything), the way it is written still disambiguates it. This is a significant difference from alphabetic languages, and of course, this poses a rather massive hurdle to language learning. After all, if you're learning English, then all you need to learn is the 26 letters of the English alphabet, and you more or less can read things. But in Chinese, there are thousands of characters that one needs to know in order to be barely proficient. I can imagine this makes it hard for the second-language learner (and this is also where my knowledge of Japanese came very handy).
So yeah, Chinese is difficult, but not in all aspects. As with every language, second-language learners just need to persevere and get exposed, and proficiency can be achieved. Let's see how far I can carry this forward.
