D may be more "complete" as it is older.
Nim has compile time function execution and Mixins, but D's Mixins may be different, I don't know. Static ifs -- maybe that is what Nims when expression is. From the current version of the book it may be not possible to learn all the advanced stuff of Nim, you may also consult the manual and read the forum postings of the smart people in the last years.
