It was nice to see David Tennant back as the 10th Doctor, but I feel he was very underutilized. Sure, his involvement helped link the Zygon plot between the two time periods at the beginning, and his relationship with Elizabeth I was expanded a bit more, but most of the time, he just sort of lingered around, and aside from Elizabeth I and the other Doctors, he didn't really interact with anyone or anything unless the other two Doctors were involved, and when he did, it was usually brief. Really, he doesn't seem to do anything of much note as an individual other than bumble around, and though funny in some places, it's quite sad that after all the hype surrounding his brief return, the 11th and War Doctors were the undisputed stars of the entire show, while the still extremely popular 10th was mostly the tagalong comic relief.
I was also disappointed that, once again, the sonic screwdriver becomes the deus ex machina with with the "same tech, new case" thing, meaning that despite the fact that many of the previous screwdrivers were destroyed, the new ones still continued any of their very long, multi-century spanning scans uninterrupted, and thus, solving all the normally unsolvable problems here because War Doctor scanned something first, and the scans would be done by the time the 11th's screwdriver came around (and still scanning on 10th's, once again making him technically useless, as the situations would still have been resolved whether he was there or not)
I am very nervous, curious, and excited about the change in plot that Gallifrey's return will bring about. I hope it will bring about the return of the Master. But then again, this new change would seem to overwrite many of the events in "The End of Time", and it creates many loopholes and continuity errors in many other stories in the revived series, especially all of the ones relating to the 11th Doctor, as he wouldn't have come about without the events from TEoT taking place. None of that was touched upon here, but hopefully, it will be in the future.