A comparison of the big three Haskell web frameworks on the most informative two axes I can think of.

image/svg+xml DSLs Combinators Snap Happstack Yesod NS Some things dynamic Everything type-safe

Note that this is not intended to be a definitive statement of what is and isn't possible in each of these frameworks. As I've written elsewhere, most of the features of each of the frameworks are interchangeable and can be mixed and matched. The idea of this matrix is to reflect the general attitude each of the frameworks seem to be taking, because sometimes generalizations are useful.