It depends on whom you ask.

As a person who doesn't even know what language this is written in, I don't think it is readable at all. For example, this "Select(i => i + 2)" piece looks totally strange for me. What does it do?

After learned Lisp, I feel there's too much syntax to learn for non-lisp languages. Every language introduces some idiosyncratic syntax. Life is too short, I just don't want to learn syntax that someone else invented to just be able to say "this is different".

In clojure you would typically write it as:

   (->>
       (range 10)
       (map #(+ % 2))
       (reduce +))

Which is just as readable as the .net equivalent.

And I prefer

    sum(i + 2 for i in range(1, 10))

for readability. But we shouldn't judge languages on this sort of thing -- because then why don't we just write sum(range(3, 12)), or 63?