The action for the last two episodes switches to the Shadow planet for the last two episodes, which is a welcome relief if only because it limits the involvement of Merak (and Shapp, too, who has been painted in broad, comic strokes, but has been entertaining, none the less).
There's a quite chilling scene, actually, when The Doctor is communicating with the Shadow and explicitly mentions his task of finding the Key to Time on behalf of the White Guardian. The Doctor has been quite keen on keeping his quest secret (including, at times, to Romana), so to see him mention it here raises the stakes a bit, and again flirts with creating some good, solid drama in a story that has been frantically searching for it.
But then The Doctor, unconvincingly, gets sucked down a hole (apparently, anyway. The effect portraying this is ambiguous, at best) and meets up with Drax. Drax is on the used car salesman end of the Time Lord spectrum, apparently knows The Doctor from the Academy days on Gallifrey, and is another comic relief character intent on diminishing the drama. Drax is also another nail in the coffin that is the mystery of The Doctor and Gallifrey - he's just your average Time Lord who's trying to make a living. Plus, we know the year (well, at least the last two digits) of when The Doctor went to the Academy. The image of a young First Doctor rushing off to class after getting rip roaring drunk at a kegger the night before is now prominently affixed in my brain.