In Perl, I find metaprogramming to be extremely powerful. I don't go too deep into Class::MOP usually. However, I do find that focusing on tooling before code is usually a net win. This means a lot of work can be done by writing DSL's that use metaprogramming behind the scenes. It works well and has become a common approach for certain kind of things (like object frameworks).
I'm not saying you should never use metaprogramming. Sometimes there is no other (practical) way. But it can be easily abused, often for a little added convenience but a much larger conceptual complexity and additional debugging issues. Why have a well-designed API when you can have a metaprogrammmed mess instead?
