Apologies in advance as I have nobody in real life to talk to about this, so I'm just going to ramble!
I loved the book and the first season, and I think the partnership between Crowley and Aziraphale was definitely the high point in both, but there were lots of other well-drawn characters there to balance it out. It feels a bit self-indulgent to focus on them so much this season, especially in the flashback scenes, which felt quite overlong in places. I think they could have made the same points in a much more succinct way. Aside from the angel Muriel (whom I really liked), I didn't really feel like any of the newer characters were interesting or fun enough to balance them this time around. The Nina and Maggie relationship didn't seem to have any depth to it; I guess maybe that was kind of the point, that it was just being used as a proxy for Aziraphale and Crowley, and I liked that they were called out on that at the end of the series, but it still felt quite contrived.
I loved the opening scene seeing Crowley as an angel. I also loved Aziraphale driving the Bentley and his acknowledgement that he lets Crowley rescue him because it makes him happy. I think I prefer stuff like that when the insight into their dynamic is a bit more subtle, as it was in the first season.
I don't know how I feel about the ending. It seems to undo so much of Aziraphale's character development from the first season where he slowly comes to realise that Heaven isn't all it's cracked up to be and he and Crowley decide they're on their own side. It feels like a bit of a cheap reason to create drama and heartbreak and make people demand a third season in a way that doesn't seem to fit the characters. Maybe it will make more sense if they do get to explain it in season 3?