1)Well, now we get the new show's take on a perennial of the old show, the "base under siege" story, with a diverse bunch of characters in an isolated situation being picked off one by one by an ibnsidious threat. I always liked these kinds of stories, and this one is a good one. Added to that, we get to see the Doctor react to challenges to his fundamental beliefs about the nature of the universe.
2)Having recently re-visited their neighbors the Sensorites, we get to meet the Ood, who like them, look like a Doctor Who "monster", but are in fact, more abused by humanity than a threat to them. As an underclass oppressed by human masters, they actually remind me a bit of The Mole People. They managed to be creepy and sympathetic at the same time.
3)I liked Tennant's work in this - especially his horrified reaction once he believes the TARDIS is lost and he might have to live a normal life. I've always suspected that deep down inside, the Doctor's greatest fear is that someone would force him to get a job and work for a living. I also liked seeing the Doctor seeming a bit timid for the first time ever.
4)I have to admit that when I first saw this, I did not make the connection that the guy who does the voice of the Beast in this was the same guy as played Sutekh back in "Pyramids of Mars". Nice bit of casting, that. The CGI "devil" was reasonably well-achieved, too.
5)Will Thorp did a very good job as Toby, too. Very well acted.
6)Funny how much the seal of the Pit looks like a giant manhole cover.
7)Some choice overacting from Tyler, here, but not really out of character. I did like her reaction to being called "the valiant child who will die in battle". That would be enough to creep anyone out.
8)Cliffhanger: "The Pit is open and I am free!" Resolution: Nothing comes out. Kind of an anticlimax, really.
Some Fun Quotes:
Overall: I quite enjoyed. I thought it was well-written and well-acted. The Beast was quite a scary adversary for the Doctor.