I think that's a bit harsh calling it a joke...!!!
I dunno, look at the state of some of the vocabulary and language used - it's just completely out of date. I suppose - it's not absolutely dreadful if you can laugh at it and point out obvious nonsense.
I taught this for four years when and it does have its place in teaching English up to a pre-intermediate level, but, as many have said before and do themselves it should be dropped after say stage 7, because the rest of it is written as an after thought with no clear direction.
I wouldn't even go so far - stage 4 would be enough in my book. You can see that he had the right idea for the first couple of books, but then he had the obvious "oh ****, now what?" moment - the way the grammar is presented/taught is just mindblowingly idiotic and confusing.
I do know however of many students who have become successful users of English through this method and doesn't deserve the label of being classed as a 'joke'.
From what I've found, it's good for people who want to use it as a base for learning - but the claim that "you don't need another book" is just widely inaccurate. When I had the misfortune of using it, I used to supplement it with all sorts of extra materials - and that worked quite well for beginners.
Mind you, I think it's a good way to judge a school - if they stubbornly insist on sticking to "the method" - then the chances are that they'll be utter crap. And the less said about Callan training "courses", the better ;)
(I had the misfortune of being convinced to go to one because the school wanted to appraise them - resulted in a full day of me and a couple of Polish teachers abusing the trainer by asking difficult questions)