I've skimmed through most of the comments posted at the link Bella provided. There are a lot of interesting comments there.
I've also watched a lot of his shows. I see a lot of common sense in his approaches to dealing with difficult behaviours (humans as well as dogs) but I think if I were to have one main criticism of his show is that it seems to me that along with his many years of familiarity with dogs of all kinds (breeds and behaviours) one of the reasons why his techniques work initially, but sometimes then fails, is because he has a presence about him that animals recognise. One of the examples of this is when he goes into a house where there's a dog that behaves badly towards strangers, and that dog doesn't react the same way towards CM. It seems he gives off different vibes from the owners, probably because of his years of experience and his self-confidence - something that some owners can have difficulty reproducing.
I also find it interesting how he gets the point across to owners to pay attention to their own behaviour, that their body language is something that a dog will pick up on. It's also interesting how quickly he controls dogs that rush to the front door and how he appears to do that simply by his presence. A lot of the episodes show how people can learn that themselves, because they see how it's done.
I wouldn't regard him as a dog trainer, per se, because he doesn't use verbal commands. I think he gives people a good insight into the relationship between human and dog. I wouldn't criticise him for using the term "pack leader", because that's a term that most people can understand. It's not totally about who's "top dog" or whatever, but it is about who is ultimately responsible for the welfare of all creatures in a household, and that has to be a human.
Also, I can't see (and haven't seen) how he could be using cruel techniques - he would have gone out of business a long time ago if that was the case.