Being able to use the web as "just another platform" and use a single unified codebase across all platforms is a killer feature, especially for games. Also, maybe I'm old-fashioned, but I'd rather do a team-project with a "million-lines-of-code" in a compiled language with static type system which gives me compile and linker errors if someone adds a new function arg or changes the type of an arg. Of course also with other "compiled-to-JS" languages, but the killer-feature is multi-platform from the same codebase.