I think you don't have to read The Search, it wasn't good.
I'm glad they didn't go through with Zuko not being related to Ozai--that would have been thematically terrible. I liked the spirit. Everything else was unsatisfying, bad, boring. So Ursa didn't leave the fire nation, she just abandoned her kids as completely as she possibly could. It should have been easy to make this compelling. It starts by introducing us to Ursa and Ozais marriage being a nonconcensual arranged marriage, and a post mortem revenge against Romu's bloodline, adding layers to the terrible abuse in the royal family. But then they have this boring journey where the Gaang act like they didn't have any character development. Also they wrote azula as an actual monster even as a small child rather than a victim of her father's abuse like Zuko. Pretty shallow, doesn't seem to fit with the themes of the show. The face spirit looked cool and that's the best thing about this. The worst part is that Ursa doesn't leave the fire nation she just decides to change her face and forget about her children, consciously choosing to abandon them even in her own mind. Wow, so cool. Yeah I'm just going to pretend I didn't read this.