I got the hardback edition in the mail and finished reading it today.
The art ranged from awful (Fifth, Eighth) to great (Second, Sixth, the final three issues), but story is where it was rather lacking. Aside from the fact that I was spoiled that Adam was the big baddie, I found the plot to be predictable and often boring. Some of the individual romps were engaging (Second, Third, Sixth), others didn't seem to have any point (Fifth), and a few needed another revision or two because of poor pacing (First, Fourth). Additionally, as Allyn noted with the first issue, I felt most of them didn't really invoke that particular era at all, even if the dialogue was spot-on (Second, Third, Fourth, Sixth, Tenth). Lastly, I agree that the final page was unearned and completely out of place. I can see Rose and The Ninth Doctor mourning for Adam's death, but certainly not all of the other companions and the proceeding Doctors, and to call him "One True Companion" makes no sense whatsoever.
I know I sound very harsh on this series, especially considering how much I love The Forgotten (and I know many people didn't like it), but I felt like The Forgotten had more interesting themes and captured the individual eras better than this series.
Overall, an enjoyable read, but it's kind of sad that I got more enjoyment out of visual gags like "Just Police Boxes," "Babel Fish Aquarium" and "The lunatic is on the grass" than the actual series.