Play is really not a large amount of code though and it's all in one source tree. It generally doesn't have a lot of "layers" compared to even something like Tomcat; the stack just doesn't get as deep. I've had an easy time digging in to the Play source code when needed.

Just one experience fwiw. Sure, it's still a framework.

Agreed. I fixed a handful of bugs in Play 2 while it was still young and immature and didn't have much difficulty tracking them down despite not knowing any Scala.

Despite the propaganda Scala's pretty easy to read.

I just fail to see much in these frameworks that isn't either trivial or unnecessary or both. But I didn't mean to single out Play by any means.