My thoughts: John Simm makes a superb Master, re-imagined younger, much more dynamic and madder than ever, but still just about consistent with the Master of the old series. There are other great ideas and moments throughout the story - the identity of the "ultimate monsters" which is beautifully set up in the first of the three episodes, the elaborate double-bluffs around the legend of Martha Jones and her plan - and the sound of drums itself. Is it evidence of a Time Lord heart disease, the sound of the Vortex, or is the Master just listening to the title music? I also feel I've waited a long time for those flashbacks to Gallifrey and the Citadel, and for that throwaway explanation of the mysterious Face of Boe. Martha's departure at the end is very well handled - throughout the new series the relationship between the Doctor and his various companions has been explored intelligently (this was a blind spot for the old series).
However the script is uneven and disappointing in places. The religious themes in the conclusion were overcooked - perhaps an attempt to recreate the Bad Wolf moment but this time there wasn't any of the sheer alien-ness that made the first series' climax so powerful.