CMake is a nightmare of implied complexity. I've run into multiple situations (usually but not always involving cross-compilation) where it was simply incomprehensible. No amount of time invested would let me figure out why CMake blew up. There is no way I can build something a little out of the ordinary on top of CMake and be confident that it's solid. It's just too complicated.

This sort of balancing, upfront ease of use vs hidden complexity comes up often and I have been burned enough in the past that experience dictates to pretty much always go for model simplicity and pay the upfront costs. I don't see this often however. A lot of the time people will go for what feels or looks right, superficially, without bothering to look beneath the surface or think about model complexity costs. It's an attitude that has led to many disasters in this space.

What would you gain if you're using it for other, less supported languages, like Javascript?

This tutorial was making the rounds (on HN and elsewhere) last week, but in case anyone missed it, here's a link: https://github.com/pyk/cmake-tutorial I found it to be a great primer/refresher.