I think one of the very good features of D is that it provides a lot of infrastructure that helps with lots of little generic things -- things that are not really needed in the language, but help reduce the amount of code you write or simplify common actions you take. It seems like Walter (and all the other contributors) have distilled their experience writing programs into creating a language that helps a lot with some of these things.
Stuff that I particularly like.
Assert/Enforce: http://ddili.org/ders/d.en/assert.html , Unit testing: http://ddili.org/ders/d.en/unit_testing.html , Contract programming help: http://ddili.org/ders/d.en/contracts.html, and http://ddili.org/ders/d.en/invariant.html , Scope (love this): http://ddili.org/ders/d.en/scope.html
And the other usuals -- templates, mixins, etc....
BTW, I mostly use D as a better C than as a better C++...