This one is most notable for the biggest stunt casting event ever and its massive cliffhanger. Wow.
My favorite bits were when the Doctor first sees Davros (Julian Bleach is marvelous!) and Donna brings him out of what seems to be a brief PTSD trance; and when the various guests, particularly Sarah Jane, first hear the Dalek voices and know what they're facing. ZOMG Elisabeth Sladen rocks.
Alas, Harriet Jones! But I am so glad she went down fighting, and with dignity! We shall overlook the stupid joke repetition of "We know who you are."
If I hadn't known that David Tennant was contracted for next season already, the cliffhanger would have been even more effective.