D has a built-in GC by default and doesn't force you to manage memory like Rust. Also, the author mentioned that D is pretty straightforward to anyone with some basic programming knowledge (think C, C++, Java, and C# which fits the majority of coders). Rust is very different from those languages. My main goto language is Python and I can understand D a lot more than Rust which confuses me to no end (disclaimer: I'm a total noob).
Go is probably as easy to read as D if not more and is also GC and fast. It is also very spartan. I bet D has a lot of additional features.
Go is okay but you can't get clever with it. You're productive from the start butit becomes routine quite fast and at a certain point there isn't anything new to learn. Error checking is also quite annoying.
D has the best of both worlds and it also plays nicely with C/C++, something that the author of Zig also understood is a must have in any language that aims to be a better C/C++. In D one is productive from the start and there's always something new to learn. And one learns it as they code, without having to first read Programming in D by Ali Çehreli to make any sense of the language.
I also tried Crystal and liked it but one is more productive in D and Go without any prior knowledge of those languages. I was kind of annoyed by the fact that Crystal removed the for loop, which works perfectly fine in Ruby.
Don't get me wrong, I like a language with a Gc by default, my favourite language is OCaml, but I can't claim it to be a drop-in replacement for C projects. Go, Rust (or D) stand a better chance at that.