Lua is a really simple language, and is quite malleable to different use cases not included in the language per se. Usually in my book, it is an advantage, for example how many Lisps can implement new features that seem like language features, but aren't.
But this simplicity can have a downside, as there might not be canonical ways of doing things that users are accustomed to. For example, object orientation. It could be a hard sell to someone coming from an object-oriented language, when you have to understand, and choose between multiple different styles of object-orientation and implement them consistently in your project, or use one of the many libraries made just for this. For example, see http://lua-users.org/wiki/ObjectOrientedProgramming
It is a bit nice to not be limited by any particular OO system. I don't get much use out of this, since my current class.lua is about 14 lines and doesn't do inheritance, but it would be easy to add in the future. It's probably a bit easier for people with js experience to get used to OO in Lua. Coming from js, most of the language just seems like a copy with more expressive power and fewer mistakes.
But this simplicity can have a downside, as there might not be canonical ways of doing things that users are accustomed to. For example, object orientation. It could be a hard sell to someone coming from an object-oriented language, when you have to understand, and choose between multiple different styles of object-orientation and implement them consistently in your project, or use one of the many libraries made just for this. For example, see http://lua-users.org/wiki/ObjectOrientedProgramming
Lua really is simple, but it not always easy.