I also think that Lua has a perception of being an embedded-only language (which it's very good at). The biggest code bases are World of Warcraft interface modifications and other plugin architectures. The features Lua would need to be really competitive as a stand-alone language (ex: good library management[1]) are still developing. I think it has the potential to be very powerful, though.

If you want to have some fun with Lua, check out LÖVE[2].

[1] http://lua-users.org/wiki/LuaModuleFunctionCritiqued [2] https://love2d.org/