Ruby's main advantage is that they've nailed the syntax sugar in all the right places. For example, given function foo:

 foo()

is equivilant to

 foo

Also, code blocks are specified outside the function argument list. Something that looks like this in javascript:

  foo(a,b,c,d,function() {
    console.log("some callback")
  })

would look like this in Ruby:

  foo(a,b,c,d) do 
    puts "some callback"
  end

or even just:

  foo(a,b,c,d) { puts "some callback" }

That last one isn't a function definition.. it's a function call equivalent to the example before it.

It's mostly the fact that it -looks- cleaner in all the right places that makes it appealing. That and the massively powerful web framework built on top of it.