Lua is the preferred language to add scripting into games, there are even game engines like Corona or Love2D which work exclusively with Lua.

Personally, I dislike some portions of the language (ex. the standard library forcing you to use arrays initialized at 1), or how easy you can break block comments with nested arrays.

In my personal projects I tend to favor Duktape, which is a lightweight JavaScript Engine meant for embedding (the same use-case as Lua), but people who love Lua usually hate JavaScript passionately :P