I dove deep into Scala a short while back and I can concur with those that thought the documentation was sub-par almost all around, from Scala-Lang site itself,

I dove deep into Scala a short while back and I can concur with those that thought the documentation was sub-par almost all around, from Scala-Lang site itself, to big things like Play Framework to across small userland libraries. The saddest thing was that I wanted to improve those docs, but I didn't know how. When I finally got to the point through tedious trial and error, I couldn't even remember where to start. It doesn't help that there's 10 ways in Scala to do everything, but no way to find out which is the best one, or the worst, or one that even just works with your current version. Surely this the tone of this post is quite whiny, but it really did make Scala hard as hell to approach.