The addition of hot reload of extensions finally makes C++ programming on the new Godot bearable. It was a deal breaker when I touched the game engine from 4.1 and this release delievered exactly what I wanted.
The editor restarts fast enough that, for me, it was a tolerable part of the iteration process. But yeah this is a massive improvement; GDExtension is a really important part of what makes Godot attractive for serious game development.