I thought that let looked odd, because I thought that with a let in arc, you had 1 variable/value pair. Thanks, zck, for pointing out the difference. And thanks, akkartik, for repeatedly telling me this.
As long as you use '=' it's easy to keep programming C or MUMPS in Lisp. Avoiding '=' forces you to give up old habits and become fluent with (writing as well as reading) deeply nested calls, 'let' and recursion. Those are some big reasons to use Lisp rather than imperative languages. So if you don't use them you're missing out.