Elm is very cool and pleasant to use compared to JavaScript, but I have some reservations. The limited typeclass system (for numbers and such) seems... questionable. The interaction of what looks like pure declarative syntax and what is actually impure imperative semantics is confusing to me. I understand that the author wants to avoid monads and other perhaps somewhat confusing staples of functional IO, but I'm not sure the cost/benefit of doing it this way works out.

I will say that Elm is the best JavaScript-targeting platform I have tried! I have hopes for GHCJS, but it's not near Elm's level of readiness yet.