The topic of s-expressions, indentation-based alternatives, etc. comes up so often that I wrote up my thoughts at http://chriswarbo.net/blog/2017-08-29-s_expressions.html

tl;dr the killer feature of s-expressions is that they're trivial to parse and generate, which makes it easy to read/write some other "front end" instead (i-expressions, sweet expressions, wisp, etc.).