Not all of them are great--I think the 70s one is kind of spotty, myself.
And I think the format has limitations, though I "get" the reason why. Simple, regular panel layouts(the same each page) and content-first in order to appeal to the casual trivia impulse-book reader--according to a friend who contributed to that one, it's not at all meant for people who are regular comics readers.
Which is fine, it's just that one must keep that in mind when reading them. They're meant as broad surveys of their subject, and at first I mistook this as shallowness. (in some cases, I think Vankin IS a bit shallow in his treatment, but not overall).