In what way? It uses an alphabet just like Latin-based languages, and it's more phonetic than English (but not completely phonetic). I'm sure anyone can learn to write/read Cyrillic in a few days if they already know Latin. The actual language is harder than English because of large number of noun/adjective declensions (depending on plurality, case, gender) which would be a pain to memorize for a non-native. But being an Indo-European language it's still pretty similar to English as far as languages go. Chinese, having a completely different writing system, completely different sentence structure, completely different fixed expressions, completely different sounds (and tones!) is orders of magnitude harder.
My wife knows Russian and 5-6 other languages on a tourist level or better. She says Russian has both a difficult and a simple aspect: Newspapers use a large vocabulary so reading with moderate education is tricky, but people's accents are easier to deal with.
I don’t think anyone claims that spoken Chinese is particularly hard compared to other languages, but that the written form is measurably harder than languages that use an alphabetic orthography.
(I have read claims that Russian is particularly difficult though - can anyone comment?)