Overall, I had mixed feelings about this episode. At times, visually speaking, the episode did remarkably well at fitting the Doctor Who format. The sisterhood echoed the sisterhood from the Fourth Doctor episode "The Brain of Morbius." The setting was well done, but the episode did frequently overdo the CGI a bit.
The pacing of the episode felt a bit rushed to me, as the first half was laying the groundwork for the rest of the episode, but it seemed like the history of the sisterhood, and the activities in Caecillius' house always felt a bit rushed, as if the story was in a hurry to get to the volcano scenes.
Once the Doctor and Donna were in the volcano, the episode rapidly began to lose Who points - the visuals turned into a CGI-fest, and the music turned into a full blown orchestra meant for the motion picture "Dante's Peak." The drama from this point on doesn't just go overboard - it goes bonafide bananas. Donna tears up, yells at the Doctor in and outside the TARDIS.
Additionally, some of the dialogue was ripped from modern-day behavior for Caecillius' teenage son, Quintus. For example, Quintus telling his parents to "get off" was a phrase unheard of during that time period. Another example was the Stallholder's reaction to Donna attempting to speak in Latin - a modern day smart alec response, "Me no speak Celtic."
The final scene to me was absolutely pointless - that of Caecillius' family living a normal life six months after the destruction of Pompeii, where Quintus is shown giving thanks to an engraving of their house gods - the likeness of The Doctor, Donna and the TARDIS.
An OK episode - the plotline was relatively good, but the episode just seemed to be hyped up big time with blasting choral and orchestral music throughout the entire length of the episode (save for one or two dialogue scenes), and the acting and drama just was way overboard, designed to make the fan girlies choke up at Tennant's tough decision.