Absolutely horrible. Intended as a replacement for the ExtUtils::MakeMaker, but does not replicate EU::MM's install options, nor fully document its differences. After ten years of using it, I am sick of modules which use Build.PL failing to install, or build into Debian packages due to permissions errors.
After a decade, you've had long enough to prove perl can do everything make can seamlessly. It can't, or at least your implementation can't. Make works. This module feels as though it exists out of an ideological purity, rather than any technical superiority to EU::MM.
If you are a module author, using this module is trading the users of your module's ease of use for your own. I would discourage any module authors from using Module::Build in the strongest possible terms.