I think it's definitely possible to put knowledge of Haskell to use in PureScript, but it's not like Fay, Haste, GHCJS etc. where you can copy code verbatim. I think of PureScript as "an environment in which to write principled JavaScript". That requires that, to a certain extent, you should have JavaScript's semantics in the back of your mind while developing. For that price, you get ease of debugging and some tools which you don't have in many other compile-to-JS languages (an expressive type system, type classes, ability to refactor with confidence etc.)

Of course, one of the best things about AltJS is the interoperability with other languages. PureScript won't be the best tool for every case, but it has a simple FFI. It's possible to write complete front-ends in PureScript, but I'd love to see more examples where PureScript is used alongside something else (I've used TypeScript with PureScript successfully, for example).