I thought The Beast Below was an excellent and thought-provoking episode.
It had plenty of moments to inspire wonder, laughter, or fist-pumps while yelling "hell, yeah!", but it had a dark side that reassured me that the Moffat era won't be all TARDIS Teens Fun Hour all the time. That's good. We needed a dose of lightness after the emo that Ten ran into toward the end, but part of why this show tugs on my heartstrings so much is the sad edge to the jolly mad man with a box.
Liz Ten is utterly fantastic and badass. She goes undercover (in a mask that she's apparently been wearing for centuries...I suspect that no one is fooled); she shoots things; she investigates the mysterious evil that gnaws at the heart of her nation. She looks utterly gorgeous. She also references Ten's EoT remark about Queen Elizabeth I, making me sporfle. I suppose Liz One must have left some monarch's eyes only record of what happened. Oh my! Her awesomeness would have been verging on Sue-hood, until we find out that she, like all the other citizens, has chosen to forget and make herself complicit in the torture and enslavement of the beast. She did it to save the lives of her people (btw, when did that become the Queen's job and not the job of elected officials?), but it is still horrible. The moral grayness makes her more interesting as a character. I want to see her again, possibly making totally badass babies with Jack Harkness.
Second, star whale? That name makes it hard to take seriously. Make up a frickin' word, and if you must say that it's "like a star whale" so viewers understand, but mostly call it by an original name that doesn't sound so New Age. Anything that lives in deep space obviously has no phylogenetic relation to actual whales. Also in the subject of not treating viewers like idiots, we really didn't need the sledgehammer explanation in front of the window explicitly telling us how the Doctor was like the star whale. We all picked that up the first time, in the Tower. The hug was sweet, though.
Third, did anyone watching not think of the Star Wars trash compactor scene when Amy and the Doctor fell down the chute into the goopy mouth? Obvious reference is obvious.
Now, a bit of meta. "The Beast Below" is definitely reminiscent of a lot of RTD-era episodes: Planet of the Ood, The Long Game, Gridlock, Torchwood's Meat, and more. However, the revelations and choices in the Tower reminded me chiefly of CoE. The leaders of Starship Britain (or whatever they were calling it) are faced with an impossible choice between condemning something innocent (the star whale, 10% of Earth's children) to agony, or the annihilation of everyone. They make a choice, perhaps the only one they can, but maintaining the lie to cover what they've done is doing terrible things to their nation. A hero comes along, finds out the truth, and determines to find a third way out of this impossible choice. However, the only possible other option he can find is to sacrifice a single innocent life. The needs of the many outweigh the needs of the few, and the needs of the few outweigh the needs of the one, but this sacrifice is still so terrible that it will stain his soul and alter who he is, because the one he is sacrificing is the hero's own kin. (It's emotional rather than literal kinship in the Doctor's case, but that's just as binding.) Still, the hero will make the sacrifice. What else can he do?
For Jack Harkness, nothing. The Doctor didn't come, and all the magic of Jack's immortality couldn't change the fact that Steven had to die. The universe was, for once, far kinder to Doctor. Along comes Amy Pond, a girl in her nightie, and she says no, there is a fourth way. Doctor Who is different from Torchwood. It offers room for the sort of transcendent love that would move the last of the star whales to carry an entire country of humans across the stars, and to continue doing so even after they repaid its kindness with torture. It's the same sort of love that means that even after this latest reminder of how nasty humans can be the Doctor will keep on saving Earth.
It's important that it was Amy who saw the way out, not the Doctor. The Doctor is powerful, and sometimes the only solutions he can see are the ones that involve exercising power. When one of your titles is Destroyer of Worlds, sometimes you get a bit too focused on the big picture. We saw in Waters of Mars how dangerous his tendency to exercise power and take decisions into his own hands can become if unchecked. Amy, the girl who was left behind, understands that sometimes you have to let go and trust. Humans have this ability sometimes. Rose looked into the TARDIS and trusted that it would not consume her before giving her a chance to save the Doctor, and so the Bad Wolf found a way around the Doctor's impossible choice of whether to sacrifice the Earth or let the Daleks run free. Without the Doctor, though, humans keep choosing the way that would save their sanity and their skins at the expense of their souls. Amy initially chose to make herself complicit in the sin and walk away, not seeing the way out until the Doctor's own words helped her realize the better solution. It's the interplay between Doctor and Companion (Time Lord and human, heaven and Earth) that gives this show its power.
Finally, Matt Smith is very much the Doctor. <3