Nice cheat sheet (in PDF format) for the new stuff in Unity 5 — most of it is 3D-related, but there’s still some good info for us 2D game developers… Tips and Training for Unity 5 Features
While there’s a ton of Unity info online it’s hard to know what’s worth your time. And a lot of it is aimed at people doing 3D games, not 2D.
The resources shown here are at the very least “pretty good” and they’re all focused on 2D game dev with Unity. (Or, if 3D-based, they have obvious 2D ramifications.)