It was good for what it was, but it really was just a stand alone episode. Fun, and that's sort of about it. Nice idea to try and explain why Agatha Christie lost her memory, but it didn't really explain why she lost 10 days.
I mean, yes, I get that the Doctor would have taken her in the Tardis, but why? It would have been a bit more satisfying if the adventure itself had taken place in the missing ten days, tbh.
So yeah, I'm nitpicking, and if I'm nitpicking, it probably means it's not going to be a favourite. But I've only seen it the once.
I did love the Doctor saying 'ginger beer!' to the gay footman. That got a guffaw from me, and I'm normally so very laydy-loik.