[codeflo]

Unions, generics, required fields, default values, enums that don't pollute the global namespace are things that immediately caught my eye. I assume it also doesn't repeat Protobuf's the mistake of not being able to distinguish between a missing string value and an empty string value.

Protobuf is old, and has some really strange warts that are only explainable historically (for example, by reference to the behavior of C++, which used to be Protobuf's primary target).