Those are all great languages. Haskell by no means has a monopoly on mind expanding features. But I think that the enforced purity of Haskell along with laziness and the powerful type system is a particularly brain twisting mix.
I believe this too. Presuming that functional programming is a good thing, Haskell is a great way to learn it. It will force you to operate in a functional way all the time, thus speeding up your learning process.