It was okay- the whole episode reminded me too much of the two-part Impossible Planet/Satan Pit arc from last season, which I felt was far better handled. I expect part of it has to do with the nature of the plot- people trapped in confined space, deal with threat. That's one of the shortcomings, I've noticed, of the new series' off-Earth plots for the most part- they feel so much more confined by their sets than I remember the old series interplanetary stories did (then again, its been awhile since I watched any of those, so it could just be nostalgia talking).
It did have some good bits- the Doctor and Martha, obviously, as others have mentioned, and the increasing mystery behind the enigmatic Mr. Saxon.
Previews seemed kind of blah to me, but I guess we'll see when we see. I think I'm just getting antsy for Captain Jack's return and the payoff on the Saxon plot.