>>7
It depends. If you already speak a Roman language, it can be fairly easy. Even with English, knowing that a lot of your "more-than-three-syllables" words are almost the same in French but more common, you already have an innate amount of vocabulary.
I think the hardest is the obfuscated orthography and the legendary hard grammar.
I can say it as a fact, the majority of French don't master their own language, you can see it (alas) everywhere, from the internet to newspapers and classrooms.

The particularity of French is the irregular grammar, though. Learning the tenses for each groups of verbs is daunting and boring, you may even abandon the process when you see that irregular verbs are every-fucking-where.

My best advise to improve in French is to focus on grammar for the serious part, and for the practice, you have more than 500 years of genius literature awaiting you, from the renaissance poets and philosophers to the more modern writers.
Reading French is a very important part of learning it, for French is in my opinion much more divided between its spoken and read forms. Even for French, those that often read in their youth tend to master the language better than others.

Hope it wasn't too long or meaningless.