All other Lisp-inspired languages, including Ruby, have added one important feature by introducing their biggest restriction: they went with more complex syntax

All other Lisp-inspired languages, including Ruby, have added one important feature by introducing their biggest restriction: they went with more complex syntax abandoning Lisp's S-expressions. By doing so, they have created a substantial difference in how code and data are represented: whereas in Lisp everything, including your code, can be treated as data. This is, in my humble opinion, the biggest difference between Lisp and others.