A pretty exciting conclusion to the Once And Future arc. Although the answer that the Eleven was responsible for the degeneration weapon isn't too surprising, there are some fun callbacks to the Doctor's 1963 origins here, with the Doctor and Susan during caveman times at one point in the narrative, and references to Ian and Barbara.

It is also nice to hear Susan and River interact, given that they are technically family. It gives The Union a sort-of "Lost In Space" feel, with the Doctor, Susan, and River basically being the TARDIS team of this adventure.

I am still disappointed that it was Jacob Dudman voicing the Eleventh and Twelfth Doctors, as opposed to Matt Smith and Peter Capaldi. He does do a good job with Matt Smith, but you can really tell that his Peter Capaldi isn't the real deal.

Nice if not surprising that it was the War Doctor who was hit with the degeneration weapon. It ties in thematically with the idea of the Doctor's incarnations being mostly united, and the War Doctor being the only incarnation they openly reject.