If there's vigorous debate about what the ending means, I think that's actually a great outcome. Making people think is fine.
Absolutely. And judging by the growing length of this thread, it appears that Letts has provoked a lot of people into doing a lot of thinking--which may make his play one of the more successful of our era. Even if some of them don't think they "get" it, that's okay too. At least they're thinking about it.