The uncanny valley was a term coined by Masahiro Mori to describe human interaction with robots. He posited that, “in climbing toward the goal of making robots appear human, our affinity for them increases until we come to a valley […]”. Things in this valley (robots, but also artificial limbs), by being humanlike but cold and unmoving, evoke a visceral negative reaction. If you found The Polar Express creepy, you've experienced this valley.
I've been thinking about how the idea of an uncanny valley might apply to programming languages. On the one side of the valley, you have the (unattainable?) perfect language. On the other, you have an array of languages: some are missing features, some have inconvenient structure, some have inconsistent behavior. But we accept those quirks, find them charming even. It's easy to imagine a Lisp programmer on this side of the valley, surrounded by adorable little parentheses.
And in the middle of the valley are those languages that come close to perfect but aren't quite there. If you read my last post, I think you know at least one of the languages that I see in that valley. It has many features that I desire, but they're … not … quite … right.