Jean pointed out that there were a lot more Griffin and Sabine books, so I read them too. They're all very interesting and different to read and I like them, but I didn't love them. A nice way to spend an afternoon though. And they'd be fun to do for a book group.
There are 2 trilogies that are tied together for a total of 6 books. All are short and quick to read unless you spend a long time looking at the pictures which is totally reasonable.