They are large dogs that require a good leader. Mine have been a pleasure for the most part, I had issues with separation anxiety with one of mine. They are also a bit "funny" around people they do not know. For the most part I can have friends and family come into my home without even knocking but there are some people that they won't allow in. Mine are well socialized with other dogs as well, although my female can get possessive when it comes to toys and sticks only with animals.
Health wise, I have been fortunate with mine so far. One is five and the other nine years old and they have only been to the vet for annual check ups and shots for the most part. My nine year old has slowed down a bit but he still gets around just fine.
I think they are a great breed but they are not something to get for a first dog.