The specials are great mean to meet our favurite characters one more time, also to learn new things about their history. Few scences where already shown in the core series, for me it is an advantage, as it allows to place a situation in the time frame, and it proves that this is not completely new story out of the blue.
Art is the same, characters are the same, and sound is fine, so my enjoyment was pretty high. However it is not what I had expected from the story and it was not really interesting/intriguing for me. Not dropped after third only because there would be no sense in dropping last episode.
I don't regret watching it and totally recommend you to watch these specials, but bear in your mind it is not a whole new story, just short pictures form the past.
