The biggest for me is the fact they're rewriting the graphics stack. The churn is enough but I also just don't like "fixed"/"simplified"/"helpful" tools that hide the underlying platform. Unity's shader language is extremely ugly but at least I can use raw GLSL if I have to. I've had to use custom pragmas to get certain acceleration features to work on Samsung hardware that doesn't seem possible in Godot. Hopefully the updates with Vulkan will have more flexibility.

That said, for a hobby project it seems fine.