Much like Hungarian, Finnish has extremely complicated grammar. There is a variety of personal endings which help conjugate verbs, which is quite difficult when your native language is, say, English. Verbs are also influenced by the gradation of its consonants. Nouns have a variety of cases, making it hell for anyone that does not speak it.
Furthermore, it is also filled with colloquialisms, meaning that even after you have learned the language the official way, you will still have a long road ahead of you.