What's bad about pairs/ipairs? They're just iterators, and they make the "generic for" construct much more versatile. The standard library also includes two more iterators, string.gmatch() and io.lines(), which are pretty handy. I've also used iterators to implement streams (or "lazy seqs", if you will) and something akin to Python's range().

I find nothing weird about lexical scope and the 1-based arrays don't bother me at all, but iterators are awesome.

To me, Lua's most annoying feature is that tables are the only data structure. When I was first learning Lua, I thought it was pretty cool to have one and only one very versatile data structure. Nowadays, I find it's more trouble than it's worth. Indeed, the fact that pairs() and ipairs() are separate functions demonstrates that tables are a leaky abstraction: you have to constantly think about whether a table represents a hashmap or an array or both. Luckily, Lua is very extensible and there are several ways around it.

All in all, I find Lua to be an excellent language. I wrote a utility in it at work, and most of the veterans started sweating when I told them it was written in some language they'd never heard of. As soon as I showed them the code, they were visibly relieved. "We can read this and understand it," they said. Lua's readability is a big win.