I have to admit, the Impossible Planet was fully worth it's fear factor score of Beyond Fear and absolutely terrifying in a way that few thrillers are. I'm old enough to not need to hide behind the sofa, but that doesn't mean I can't be well and truely spooked, and they got the psychological horror just right in this one. They're doing well at it in this series.
The Satan Pit, on the other hand, wasn't anywhere near as scary. That's partially because I'm old enough to know that they won't do things like kill off major characters, and that the Tardis is fawkes the phoenix and hence can do whatever the plot requires. Deus Ex Machina indeed.