I thought it was a bit of a disappointing episode, but one that might get better in retrospect, depending on how the larger story plays out.
The difficulty with these stories is always in preventing the 'it was all a simulation' reveal from feeling like it invalidates the story up to that point, and this episode didn't fully manage it.
Still, I like the idea of the Doctor's simulation contacting himself, and some of the other ideas were fun too - the e-mail of Veritas felt quite similar to the e-mail of the anti-life equation in Final Crisis, and the episode had a similar sense of doomed inevitability overall. The Missy stuff was good too, even if it kept tipping its hand too much and giving away each little twist before it happened. And how many times now has Moffat used the whole 'look me up' gimmick to scare the Doctor's enemies away?
Ultimately I think it goes down as my least episode of this series so far, but one which might go up in my estimation depending on how parts two and three of the story play out.