I'm definitely biased because I love the language, but I think Go is a good place to start. The authors talk about the language design more than I've seen for other languages. The Go blog occasionally has posts like that but Russ Cox's blog is the place to go for the gnarly details. Another good place is the proposals repo, e.g. the generics proposal. I also browse issues on GitHub and look for ones with interesting discussions.

including the syntax, which I know most nerds dismiss as superficial.

Syntax is mostly irrelevant as far as what is possible with a language, but it is a critical aspect of how easy/hard it is to use a language, and most critically how easy/hard it is to read code written in that language. IMO the only thing that's more important than readability is whether the code works as intended.