I think C is a great language. It maps straightforwardly onto to the capabilities of the hardware. What I meant by calling it underpowered is that it doesn't do much to increase your power beyond freeing you from having to write assembly language.
Higher order functions and metaprogramming are the sort of things I associate with a powerful language, like Lisp. But sometimes things get so abstract you can't tell what you're looking at.
As you point out, it's easy to ruin something like a programming language while trying to improve it. (I haven't created a programming language, but I've used bad ones.)
