I wouldn't say that this arc needed to be a full series, but to have a second part? Yeah, I'd say that would've been a good idea. Structurally wise, I think the episode works, but each story beat gets brushed through quite quickly and it's a bit of a shame, because there's a lot of potential in this concept.

That being said, what we do get is lovely and works to wrap up Eleven's era well. Matt Smith is a great standout here with a more melancholic performance, as his Doctor reaches the end with a lovely farewell speech. The characterisation of Eleven here is really fantastic and the way he interacts with Clara, especially when he's old is some of the best Doctor Who.

Tasha Lem, HOWEVER, what a weird addition. I understand her on principle, but dear god, it's the same problem the Snowmen had, she is wayyy too sexualised and it ends up being uncomfortable. Moffat... just why?

I think, with any future rewatches, I will end up liking this episode more, but I will still always wish it had a bit more time put to it.