For me there are four virtues :
1) FRP. All the attempts I’ve seen to graft FRP onto existing languages have looked clunky to me – ahem … Trellis? – Requiring the explicit definition of special types of fields. This is the kind of thing that I think needs a new language feature, not a new library.
Elm-lang’s “lift” looks a much cleaner way of going about it.
2) It’s in the browser. That’s where code has to run.
3) I like the way that it reunifies the document / graphics structure back into the same file. The problem is not so much that style and content shouldn’t be separated. It’s that there are more serious divisions of modularity to respect and forcing HTML and JS into different trees of the filing system has typically pushed highly interdependent data-structure and logic too far apart. I like the ability to bring them back together for small programs.
4) Perhaps it’s a way to get familiar with and more into Haskell. Obviously it’s not full Haskell. But it seems like a way to get more into that mind-set while doing some practical work.
Of course, the proof of the pudding is in the eating. I’d better go and try something … 🙂