1. Tooling. `go build` just needs a `go.mod` file with a list of dependencies. There's no MSBUILD stuff (I think dotnet had a similar JSON file format, but then went back to MSBUILD?)
2. Runtime. I love that Go's default is static, native binaries, and that the ecosystem revolves around that. I especially love that this enables ~2mb Docker images. (I'm of the impression that you can do this in dotnet, but it's not clear to me how easy it is in practice or if there are performance tradeoffs)
3. Value types. Go doesn't have a classes; everything is a struct, and polymorphism and so on work on structs.
4. No inheritance. I'm pretty militantly opposed to inheritance. I know you don't have to use it in C#, but in Go I also don't have to deal with APIs or coworkers that assume inheritance.
That said, these aren't major things; I'm sure C# is a great language in general, and I'd definitely reach for if I wanted to make a Windows GUI app.
C# and .NET's main strength, IMO, is the web API framework and general purpose utility; everything from web apps to Unity and Godot. It's easy to start with `dotnet new webapi -minimal` will give you a scaffolded project which is pretty similar a barebones Express or Flask app. But you get much more headway and scalability and the room to layer more complexity as needed.
It's main detriment is, as you mentioned, the need for a somewhat heavy runtime and the relatively slow cold starts which make it a poor choice for things like CLI tools and serverless functions.
That said, Go is a fine language. It doesn't have exceptions last I checked, so that could be a deciding factor. Exceptions are handy in a lot of cases.
Their performance is, impressive, to say the least.