[tel]

Typing, phantom typing, straightforward lambdas, sum types, tail-recursion, direct syntax abstractions (both Lisp and Idris are great examples).

I find that metaprogramming in Ruby is a tremendous hack for getting something like syntax abstraction and something like control over evaluation order. Personally, syntax abstraction doesn't feel super important for deep or shallow embedded DSLs (though it's obvious a big deal in external DSLs if you want to walk that minefield). You need more than nothing, but making it "human language like" is ridiculous.

Controlling flow is a big part of it though. Ruby's block syntax does a lot here, but frankly functions/abstractions never feel first class in Ruby---only Objects do and Objects are too heavyweight.