Hi Michael,
I presume the difficulties English speakers and Russian speakers face are largely the same:
Pronunciation and the tones are hard to grasp at the beginning
The characters seem mindboggling to start with, but gradually you get used to them
You have almost no cognates so learning vocabulary is a slow and laborious process
There seems to be a never-ending stream of idioms, poetry and stories from Chinese history that you need to memorise to really understand everything Chinese people say
On a more advanced level, Chinese syntax, sentence structure and the subtleties of grammar are both intricate and complex, although few ever get to a level high enough to discover this. I'm only starting to understand the importance of this after over five and a half year's of study
Laurence