I did not see the plot part about the Doctor coming.. I'd never considered that he'd have ..*not typing spoiler*.. Nice twist and interestingly resolved. Actually all the paradoxes were nicely solved.. well all but one. ;)

I also liked how Nyssa named her children. ( )

This serial is absolutely made by guest voice actress Sara Douglas' turn as... well, we could almost call her the Doctor's ex-wife. This one also manages to be one of the more sophisticated Whovian explorations of the consequences of time travel. ( )