I don't think it's specifically Haskell's style of functional programming. It's just functional programming.

Any paradigm shift requires re-learning I think. I don't actually think that's particularly hard, nor do I think it means the paradigm isn't a good one, it's just an inevitable consequence of a paradigm shift. Some shifts are easier than others, if the paradigms are closer together, but functional and imperative programming are quite distant in my view.

Nevertheless, I've seen some people find this easy, others find it hard. YMMV I guess.