I also think the biggest problem they have is the lack of good documentation. I hope they make it top priority to create very simple and complete documentation.
A lack of application patterns and tooling (generators, etc). A lack of a persistent store, I found ember-data to be difficult to use and buggy, also low on documentation. Complexity around every corner: almost everything is a StateMachine. I'm betting it's an anti-pattern. Also views & templates, controller and scope between layers.
Angular still faults on a couple of these. (Tooling for one)
