I looked at lua a few months ago, and this is what I found:

• It's a neat, small language
• Variables are global by default (like in perl), but no use strict
• The "A hash and an array are the same thing" concept really needs some time to adapt
• Simple things aren't always easy, hard things not always possible

Especially the second and the last point of that list convinced me not to adapt it as a general purpose programming language.

However for the area it was designed for (being embedded in other applications) it sure is very cool and useful.