Lisp killer features were GC, good data representation, first class functions. Lua has all that and more. But its being a "thin" library over the C runtime shows through the clothes.
Lisp's killer feature is procedural macros that are extremely easy to write and debug.
Lua doesn't have such a thing, that's why Fennel was created.
Erlang also doesn't have such a thing, that's why LFE was created.
