Ignoring metatable weirdness, I think "you need to throw out most of what you know" is quite wrong.
The main thing you need to know is that Lua's table type can be numerically iterated between index 1 and the first gap where numeric index has nil value using the ipairs iterator in addition to the non-exclusively-numeric unordered pairs iterator. A common pitfall with sparse tables is that the length shortcut # returns seemingly the wrong result if you aren't aware of that first part.
Most of the difficulty writing in Lua comes from the fact that there's no first class support for OO-style Classes, so you have to fake them, and there's no standard library so you end up reinventing a lot.
But other than that, it's a dead simple language with few features.
The main thing you need to know is that Lua's table type can be numerically iterated between index 1 and the first gap where numeric index has nil value using the ipairs iterator in addition to the non-exclusively-numeric unordered pairs iterator. A common pitfall with sparse tables is that the length shortcut # returns seemingly the wrong result if you aren't aware of that first part.
Most of the difficulty writing in Lua comes from the fact that there's no first class support for OO-style Classes, so you have to fake them, and there's no standard library so you end up reinventing a lot.
But other than that, it's a dead simple language with few features.