Russian is one of the more difficult major languages to learn because of its crazy grammar (from the point of view of a native speaker of English). But grammar is only one piece of the puzzle. Another one is developing a good словарный запас (vocabulary) which means memorizing lots and lots of Russian words.
The most important thing when learning a foreign language is your mindset and motivation. Many foreign students have this idea that Russian language is tough, difficult, challenging. They struggle when they are learning it and as a result – they don’t like it. They lose interest. This is a very common tendency among language learners. Even those people who have deep interest in the language, when facing some obstacles on the way sooner or later start to consider a thought about giving up. In fact, most foreign students struggle and fail because of psychology and not because of the methods or teachers.