I'm about halfway through Part Four, and I'm enjoying it... kinda. The Doctor and Raine sure do spend a lot of time treading water plotwise, and Raine is even more generic than when Andrew Cartmel wrote her. But Klein is fantastic, and I like the Other Doctor a lot. I hope we see more of him. I'm pretty sure this could have been three discs, though; the alien incursions got a little repetitive in the middle, and there were about then scenes too many where the Doctor and Raine hung outside of the dimensions.