Two things I love about Haskell.

1. It is very terse/expressive. I can look at code I haven't touched in 6 months and still understand what it's doing. Perhaps because my code is newbie code and thus somewhat simple.

2. It is the only language that brings me back to the days of Turbo Pascal when the joy of coding came from coding itself, not from building cool things. A small but vital distinction.

That said, I rarely get to use Haskell. For most of my tasks javascript is better suited, but haskell has affected how I write javascript to a great extent.