I've learned quite a bit of D myself lately, although there's still more to go. From what I've learned so far, I would say that, while the language is great for practically anything, the compilers and libraries that are out there right now aren't the best, and so you can't ever be sure that the compiler is bug-free (it's not). For game programming, you'd need to be darn sure that garbage collection is happening correctly, for example, and that the compiler isn't incorrectly optimizing away important code... things like this might want to make you re-think using the language. However, I myself think that the language itself is the best out there (this is completely subjective), and I think the only barrier to using it is the lack of a perfect implementation, rather than the language itself.
