Hakyll will be very similar to something like Nanoc. The difference will be mainly in the language and ecosystem -- compared to normal languages Haskell is pretty weird.

That said, Haskell is also _incredibly awesome_ and especially well suited to static site generation. Plus Pandoc is possibly the best format conversion tool out there. But I would only use if if you either already know Haskell or are curious and will enjoy playing around and learning new things.