Arguably, most of the metaprogramming in D is done with templates and it comes with all the flaws of templates in C++. The error messages are long and it's hard to decipher what exactly went wrong (static asserts help a lot for this, when they actually exist). IDE support is non-existent after a certain point because IDE can't reason about code that doesn't exist yet. And code gets less self-documenting because it's all Output(T,U) foo(T, U)(T t, U u) and even the official samples use auto everywhere because it's hard to get the actual output types.

I'd say D's template error messages are much better than C++'s, because D prints the instantiation stack with exact locations in the code and the whole message is just more concise. In C++, it just prints a bunch of gibberish, and you're basically left guessing.

It is quite ridiculous to place C++ metaprogramming and D's. For one in D it's the same language and one can choose whether to execute compile time constant parts at compile time or run time. In C++ it's a completely different language that was bolted on. C++ did adopt compile time constant expressions from D though.