After all, that's kind of the point of Lua. Write all of the performance-critical / low-level stuff in C or C++, expose it to Lua, then orchestrate it from a Lua script. Lua's C API is very pleasant to use.

As a standalone scripting language, I found it rather awkward to use when compared to, say, Python or Perl. It was only when using it as an embedded scripting language (not on a game, though) that I could really see it shine.