I haven't used Lua myself, but I'm impressed by the design: it seems like an elegant version of JavaScript minus most of the really obnoxious JavaScript warts.
The tables and metatables seem particularly great: they look like a simple, elegant version of prototype-based inheritance without some of the problems JavaScript suffers. It's certainly simpler and more expressive than a class-based system.
Also, Lua is well known for having coroutines that are done correctly. That's probably not immediately useful for complete beginners, but it's certainly a nice feature when you get to it.