Okay. I'm doing my best not to go all gushing fanboy here, but...seriously, how the HELL does he do it? How does he manage to hit one out of the park every single time? And dare we hope that, two years from now, every week will give us an episode this good? (Or at least more than two a season?)
He just nails it pretty much everywhere. The setting, the monster, the imagery, the mystery. And of course, most compelling of all, at least for me and certainly from a long-term perspective, is River Song. And honestly, the idea of the Doctor encountering [spoiler]a companion he hasn't met yet[/spoiler] seems so obvious that it's a wonder nobody seems to have thought of it before.
[spoiler]It seems to contradict the Ood's foreshadowing that the Tenth Doctor was nearing the end of his run; River Song clearly recognized him. I suppose it's possible that she recognized him through some means other than his appearance and assumed he'd regenerated, but that seems a bit of a stretch. The more plausible interpretation is that the Tenth Doctor continues on as he is and takes her on as a companion, some short while after Donna's departure.[/spoiler]
(EDIT: [spoiler]You know, it's not necessarily either-or. It's quite possible that Tennant is still the Doctor by the end of Series Four but not by the beginning of Series Five. There are still those movies they're putting out next year; it's quite possible that #10 and River Song could be in those, and even possible that a significant amount of time could pass between Series Four and the movies -- hell, if he could "one year later" over the course of a single WEEK, #10 and River Song could potentially have YEARS of implied adventures in-between movies. So maybe Moffat gets his foreshadowed existing relationship between #10 and River Song, and RTD gets his foreshadowed regeneration into #11. Actually, the more I think about it, the more plausible that sounds; RTD works with Tennant until the end of his run, which is the last movie, not the series four finale, and then the Eleventh Doctor is a new toy for Moffat to play with.[/spoiler] Also, I am typing out "River Song", both names, an awful lot here. Is it a first name/last name thing, or a dual name like I've been writing it? I didn't really catch that. But "Professor River Song" makes a lot more sense than "Professor Song".)
Any way you slice it, I think it's very clear that Moffat's already laying the groundwork for his run.
And perhaps the most compelling twist would be if [spoiler]she died in next week's episode[/spoiler]. A tad predictable, perhaps, but it would certainly make things interesting when [spoiler]she showed back up[/spoiler] during his run -- something which I think is all but inevitable now.
If I had a complaint at all, it's that he overplayed his hand with the "How can somebody be dead AND saved?" bit. Think the solution to that one's fairly obvious. And even if I'm wrong, it seems like somebody should have at least suggested the obvious solution by now.
Anyway. Damn fine ep all around; looking forward to next week's.