I liked it very much. Tennant and the guy playing Wilfred Mott had some great interactions. Some excellent acting in this one. Timothy Dalton was fun to watch, though he must've had to periodically stop to pick scenery out of his teeth.
He looked like he was having a great time being all portentous and everything. (Towards the end, he started to strongly remind me of Michael Jayston as the Valeyard, for those who remember the last time we got to see Gallifrey on the series -- "Trial of a Time Lord". If ever a Doctor had a disappointing end, it was Colin Baker's Doctor, who never even really got to regenerate properly. Oh, there was a regeneration scene, but Baker wasn't in it; they used a stand-in.)
The things that annoyed me most:
* the Master's new abilities were kind of out of left field, and didn't advance the plot enough to get a free pass on that (you can get away with just about anything as long as you make it worth the audience's while to suspend their disbelief; you can't just jack around with the audience)
* Gallifrey's appearance over Earth had a large dose of Bad Astronomy -- not for its sudden appearance, which we can easily ascribe to future tech and physics beyond our current understanding (Clarke's Law and all), but for the fact that it is apparently much larger than the Earth, yet has been established as having close to Earthlike gravity, and for the fact that it should have provoked tidal devastation on a truly apocalyptic scale just by being so close; of course, one could retcon that as saying that maybe it hadn't become fully corporeal yet, but I dunno
* Every season, we seem to get one or two (usually two) global-scale apocalypses which everybody seems to blithely disregard afterwards. The same thing has been happening on Torchwood and the Sarah Jane Adventures. To borrow a line I once saw in an MST3K fanfic, this isn't suspension of disbelief. This is hanging disbelief by the neck until it is dead, dead, dead. Roger Ebert remarked that something is wrong in a movie if the characters have to be complete morons in order for the story to work. What about a show where the entire *world* is apparently populated by morons?
And last, but not least,
* The regeneration was the second silliest yet, IMHO. (Silliest, and most annoying, was the one last season. The regeneration that wasn't, aka a really dirty trick to play on the fans, and an awful rash way to get a little cliffhanger excitement.) The Doctor easily blew away old records for duration of time from mortal injury to regeneration. How mortal was that radiation injury, if he a) healed all his wounds without regenerating and b) had time for a nice jaunt around the universe, locating ways in which he could quietly help his friends by screwing around with time, before finally succumbing and turning into Matt Smith? And while we're at it, what the hell was going in that regeneration? We're not talking Highlander: the Series, here. Regenerations have never been like Quickenings. What was that all about? And blowing out the TARDIS windows? It's not even properly real! The police box is just a block-transfer mathematical model laid upon the outer plasmic shell. And if its windows really CAN be shattered, why didn't it depress at that point? Shouldn't the Doctor be rapidly running through his remaining lives as they progressively asphixiate, one after another? And since Tennant was #10, that wouldn't give him very long before we get to find out if the Valeyard really is the 13th Doctor. What's more, the whole sequence, from mortal injury to regeneration, was almost a quarter of the second part's runtime. Were they trying to pad it out or something? It was like something you'd read in a college student's first fanfic. In terms of time to die, it made "The Song of Roland" appear reasonable. (Roland takes about two dozen pages to die, after being mortally wounded by blowing his horn too hard, and during this time he slays a ridiculous number of Moors, sometimes while several are still impaled on his sword. This wasn't that absurd, except for the duration.)
I do notice one thing: since the new series started, all regenerations have occurred inside the TARDIS. That includes Eccleston -> Tennant, the Master regenerating from Derek Jacobi to John Simms, the Doctor inexplicably temporarily regenerating into himself in last season's finale, and now Tennant -> Smith. Why would that be? I can't imagine some kind of FX restriction, since the old series managed just fine on less budget and lower tech.
Fun with statistics....
During the entire run of Doctor Who, we have seen
1-2: Earth (south pole base)
2-3: Gallifrey
3-4: Earth (UNIT HQ)
4-5: Earth (Jodrell Bank, under the Lowell Telescope)
5-6: TARDIS
6-7: TARDIS
7-8: Earth (morgue)
8-9: not shown
9-10: TARDIS
10-10: TARDIS
10-11: TARDIS
Romana 1 - Romana 2: TARDIS
Delgado Master - decrepit Master: not shown, may not involve an actual regeneration
decrepit Master - Ainley Master: Traken, touching the Master's spare TARDIS but not actually in it
Ainley Master - executed Master: not shown
executed Master - Roberts Master: Earth (San Fransisco)
Roberts? Master - Jacobi Master: not shown
Jacobi Master - Simms Master: TARDIS (the Doctor's, as it happens; no regenerations have been shown in anybody else's TARDIS)
So the TARDIS does turn up disproportionately. I wonder why? As far as I can see, there's no plot reason why this should be so, and thus it seems to be just writer preference. Interestingly, the Doctor has only once regenerated on a planet other than the Earth (and that time, it was Gallifrey, in its first appearance). It further appears that only three of the Doctor's regenerations didn't involve Earth in some way.