The belatedly aired "Battlestar Galactica: The Plan" promised to reveal the Cylon side of the saga and shake the audience's perception of the entire series.
Well, the "plan" was to kill all humans in a nuclear holocaust. That didn't work, so the oft-repeated premise of "... and they have a plan" is pretty much blown out of the water. It was kind of a let-down, though anybody who had watched the entire series had pretty much figured out that "the plan", whatever it was, was poorly defined and subject to change.
"The Plan" expands upon the idea that John/#1 is the chief orchestrator of the Cylon shenanigans. We're shown glimpses of the Original/"Final" five as John/#1 tests and tortures them. They come out in a fairly positive light, as the audience had pretty much figured out by virtue of watching the entire series. We're given a half-hearted insinuation that Baltar slipped Adama the note from the beginning of the series revealing that there were only twelve Cylon models, but frankly this was too weakly suggested to give it much credence, and it really wouldn't make sense in the context of the rest of the series.
The only real, hard revelation was the idea that certain Cylons developed reservations about destroying humanity, and were more controlled by John than had previously been suggested. Manipulation aside, the moral struggle of the Cylons is pretty weak tea. After all, they do continue to hunt humanity towards extinction until the New Caprica colony is discovered, and for some time after humanity's escape.
So, the plan is that there is no plan -- just a bunch of audibles called by #1 -- and cylons #2 through 12 really aren't all that bad. What a disappointment.