The Trial of a Time Lord: Terror of the Vervoids and The Ultimate Foe.
I liked the 'who done it' aspect of Terror
but its the only thing that really works in the serial. Everybody on the ship is a suspect in the crime until the culprit is finally revealed in part four. Unfortunately none of the suspects are well developed and the serial has several subplots that lead to nowhere like Rudge and the Morgarian's plan to take over the ship. They take the ship, the Morgarians are killed, Rudge runs away and is killed by the Vervoids. That's it, all done.
I enjoyed Foe
more but I think the original ending, with the Doctor and the Valeyard plunging to their supposed doom, would've been much better. It also would've served as a better end for the Sixth Doctor than the one he gets in Time and the Rani.
The concept behind the Valeyard is interesting and I wouldn't mind it being explored further in Modern Who since Classic Who never got a chance. Since it's likely Matt Smith's tenure is almost up, we're fast approaching the time between the Doctor's 12th and 13th lives. Unfortunately I've got a feeling the Valeyard's going to be completely ignored.
I'm not too sure about Mel at the moment. So far her defining trait appears to be the ability to state the obvious.