It's a very well designed language. Authors call this 'orthogonal design'; features like iterators, meta-tables and coroutines are independent and you mix and match those to produce architecture you need. It takes some hard work to design things orthogonally, to identify and isolate usable abstractions, and then put them together in a way that has no rough edges. It seems Lua has pulled it off quite well, with very little accidental complexity.

I'm amazed the language hasn't caught on more. It's perfect for education, as it is simple to learn basics and algorithm design. It's already used in some of most popular games (Roblox, Minecraft mods, WoW...) so there's established playground for children creations. Code flows like English language (which is bad for advanced users but perfect for kids). I'd say it's more suited for education than Python because it is simpler and more transparent.

The things missing are tooling and documentation. There's only single popular IDE. The Programming in Lua book is awesome read (I'd recommend it even to non-Lua developers), but it's not a good language reference. The reference itself is quite useful but sparse on examples. I wish there was clojuredocs.org for Lua, community-sourced examples are amazing idea.