> your own example of defining an enum value

That is hardly the only place that has a constant-expression in the grammar. (BTW, D enums can also be floats, and even string literals!) You could use CTFE to initialize const floating point globals. static_assert also takes a constant-expression.

> There's just a boatload of gotchas.

The D community has 17 years experience with it. It remains an indispensable feature.

As for embedding a printf, that has come up. Recall elsewhere I said that only the path through a function has to be pure for CTFE to work, not the whole function?

    int sum(int a, int b) {
        int s = a + b;
        if (!__ctfe) printf("sum is %d\n", s);
        return s;
    }

__ctfe is a keyword that says "CTFE is executing this function".

> If you could use this feature to define huge matrices of floats, that'd be pretty cool!

I use it to statically initialize complicated tables at compile time. Before CTFE, I wrote a separate executable that would emit source code with the array initializer. I like the new way mucho bettero.

If you prefer "hideous hacks" (your words!) I won't take that away from you.