FWIW, I picked hp D ~2 months ago, and my first project was a reflection library, so I've had a chance to deal with most of the language features at least once so far. The naming and presence of legacy C++ was a little strange, but I would leave it at that. What was by FAR the most confusing/frustrating thing was the vague, and many times, completely wrong or misleading compiler error messages. If time was to be spent anywhere, I think that would be most helpful.
I would quote a few of these error messages, but I wouldn't be able to reproduce them, as I have no idea why they occurred in the first place..