They keep getting better, there's not much more to say than that about the quality of this episode. Longtime Doctor Who fans like me get treated to a return of Sarah Jane and K9 and everyone gets another action-filled, quick-paced Doctor Who adventure.
Where this episode excels over the past two is the Deus Ex Machina isn't as extreme. That is, there's always a magic bullet fix, but this one was well set up and didn't leave any aftertaste. The story flowed and it was quite interesting to watch the new companion meet the old.
Once again the episode plugs Torchwood and I'm thinking that may be our Bad Wolf of the season. You're left wondering if Sarah Jane is going to be seen on Torchwood. There's nothing on the official site about it, but you the possibility is definitely there.
In summary, great story, great plot devices, great reintroduction of an old character: This ep = A+ (100!).