I think the optional part might have a bit to do with it. In Java, C#, Go you are 'stuck' with the garbage collector, so people learned to live with it and usually realized it's not as bad as people claim it to be.
There's a few other subtle things I like about D too, like the constructor[0] for a class is just this() {} instead of SuperLongClassNameFactoryShopPlaceThing () {} so instead of being redundant with typing, you realize the constructor can just have a much more obvious name such as "this", I know Python has __init__ and the @classmethod decorator for the case where you have to 'overload' the constructor. There's also 'auto' which is similar to 'var' in C#. If you are instantiating a class, why the hell do you need to write it twice, shouldn't the compiler know already the second you invoke the class constructor that your variable will be of that type? So 'auto' is nice too. These are seemingly minor things, but being a programmer who loves programming and programming languages I appreciate language aesthetics / syntatic sugar.
Also parallel compilation is my absolute favorite. When I found that compiler flag and used it I was amazed at how fast code compiles with the D compiler.
Coincidentally I started reading on D last weekend. There are lots of things that are appealing to me (at least in theory since I haven't used them): UFCS, modules, pure, @safe, contracts, support for "D-scripts" using shebang, etc.
I just need a project and some time to play around with it, but my first impression as someone that worked with C++ and Python in the past is really positive.
Yeah I'm mostly coming from C# / Python so I absolutely love D. I'm not sure what kind of projects you're interested in working on, but if by chance they are web related (or wouldn't mind trying web development) I highly recommend Vibe.d[0] and DiamondMVC[1].
Using an OS written in a GC enabled systems language made me realize that not only it was viable, it was quite productive to work in such environments.
The problem is having a big name OS vendor willing to push it to the nameless crowds no matter what.
So far we have to get happy with half-hearted steps like Swift, ChromeOS/Android(Things) with heavily constrained NDK, .NET/UWP on Windows and maybe in a decade with more baby steps, we are able to reach what Oberon/Topaz/Spin/Inferno/Singularity/Midori had on their design.
Also parallel compilation is my absolute favorite. When I found that compiler flag and used it I was amazed at how fast code compiles with the D compiler.
[0]: https://dlang.org/spec/class.html#constructors