Overall I think it was pretty good. It takes a while to get used to the JLA continuity as opposed to JLU: there's no Hawkgirl, the GL is Kyle and not John, Superman is married to Lois and Diana is an ambassador from Themyscira rather than an exile. But I'm comfortable enough with the idea of AUs that it wasn't so bad. The writing was pretty good, although there were a couple times when the dialogue sounded rather stilted and unnatural... but that's something I've noticed in comics in general.
All of the characters except J'onn -- poor J'onn -- got a couple pages of backstory to help out the novice (which I appreciated) and a fairly significant chunk of 'screen time', although Diana was the main focus of the story. It was darker than I had expected in some places, and very humorous in others.
Probably my biggest complaint is that the story's main OC, a woman named Ana, bordered on MarySueness. All of the characters are impressed by her, Flash flirts, Kyle has the hots for her, and she kisses Bats on the cheek twice and gets him to smile... sorta. Like the author, she's an expert diver. Plus, while she's initially wowed by the idea of the JL coming to her aid, after the first few encounters she's a little bit too blase about the whole thing. There are also a couple of instances where Bats came off as a little too... gentlemanly, I guess. Maybe even a little too talkative. But that could well be something taken from the comics that wasn't transmitted to the animated series.
Anyway, overall I give it a thumbs up, especially since it seems that the author hasn't written a novel before this one... she's worked on strip comics for 25 years, but there's no mention of any other book books in her bio. That's pretty cool, then.
Next in this 'series' is Exterminators, by Christopher Golden. Any relation to Christine, I wonder ;)