Leaving aside the fact that you have at least 4 (EDIT: 5) mistakes in that code, I find it less readable than the Lisp equivalent. The brackets reinforce the structure imposed by the indentation and help me keep track of order of execution. But that's how my brain works and that's why syntax is subjective.

My apologies, it should've been (if you insist on indentation)

        let a, b, c = 0, 1, 0
    fb_start:
        writen(a)
        b +:= a
        a :=
          b - a
        c +:= 1
        if c < 100 do
          goto fb-start