I was noodling around with some Ruby the other day, and all of a sudden I ran into a situation where I wanted to do a partial function application. But how do you do that in Ruby? It can certainly be done, but it felt very awkward to me and made my code less readable than the non-partially-applied alternatives. So I didn't do it.
For me, higher-order functions in Ruby are the language's only blemish. It seems almost unfair to ding Ruby for that, because Ruby (at least since 1.9.x) does higher-order functions pretty admirably. It's just not as elegant as the rest of the language.
Ruby has set an extremely high bar. The lack of ceremony in the language makes it extremely readable. The purity of its "everything is an object" stance makes it very writable. And its pervasive methods of introspection make it amazingly powerful.
But Ruby is definitely the best language that I know.