This definitely needed to be cut into two. Peace Talks was more of a slow build with a few heist sequences. Battle Ground is a war novel. It's amazing to finally see all these factions collide like this. Ethniu herself was I think a little underwhelming, but definitely did her role in upsetting the status quo. However, if anything, I think too few named good guys died or suffered terrible fates in this book.
What's really amazing is how much more Harry and Mab's relationship is fleshed out here. I commented on it previously when I was reading through Peace Talks, but Harry has been insanely effective for Mab as her Winter Knight. He tied up the whole affair with Maeve, he helped her screw over Nicodemus, and he's apparently been getting Winter Court owed favours steadily repaid. Now he's in a sense defended Mab's honour and position as the one who pushed through the Unseelie Accords. His and her interactions throughout BG really set the stage for what's becoming more and more a partnership instead of subordinate and queen, even if Mab gets the better of him at points like with the marriage. I adore her meta-commentary near the end of the book.
Also, Harry gets to basically grab Mab roughly twice. Once early on to protect her from I think one of the assassins, and again later to protect her from rebar spears. Definitely not something he could get away with out of scenarios like this! Mab still gets to look great herself, too. She was the only one really able to go up against Ethniu alone to start, even if she could only hold out for one attack.
One more note...I borrowed this from the library and dropped it back off, and I don't have a copy of Cold Days either to compare with. But I think I remember in Cold Days that when Harry briefly went after his mantle, he keeled over because his bargain with Mab to join Winter was the only thing that kept his back healed. I'm pretty sure at least once in BG he gets his mantle cut off at least once from the presence of iron, but he doesn't keel over. Wizard healing is a lot better than normal human healing, albeit still as slow, so it's entirely conceivable that Harry's back has finally healed.
So the Fomor are basically done as a fighting force. King Corb at one point mentioned a fifth of his forces were killed, and that was before the final fight, then their retreat, then the helicopters gunning down more of the Fomor as they escape into the water. If they have any form of a written language, Ivy alone will now likely oppose them actively since they specifically attacked the mortal world. Now the Red Court has been completely annihilated, and the Fomor have been drastically reduced in number. The White Court has been mostly neutralised as a personal threat to Harry in previous books, and with his impending marriage to Lara even more so. Marcone might still hate his guts, but since Chicago as a whole is likely to band together in a weird quasi-alliance against basically the rest of the supernatural world that isn't part of the Unseelie Accords, he wouldn't get any advantage currently in having Harry killed. The Denarians aren't broken, but they've certainly been weakened - Deidre is dead, at least one coin that I recall (maybe two) are in Hades' vault, Nicodemus' squires abandoned him, and Tessa's faction will have been even more turned against him.
It makes me wonder who the next batch of enemies to take front stage will be. The Black Court has been hinted in previous books to have been mostly wiped out centuries ago with only its really wily, devious, powerful heavy-hitters remaining. I take that to mean they've also had centuries to regroup and very slowly build a power base again. The Jade Court of Vampires has only been mentioned like once before, so they may be a non-factor. I think it's more likely the Black Council of wizards and the necromancers will start to pop up again in more serious numbers, now that Nemesis has been revealed to Harry and has lost one of its major vassals.
Speaking of Nemesis, so it was forced to reveal its name as He Who Walks Beside, one of the three Walkers. He Who Walks Behind was the one that was summoned by Justin DuMorne to kill Harry, who Harry barely managed to banish, while He Who Walks Before was a major antagonist in Cold Days ('Sharkface'). But Nemesis has been a lot more subtle in its approach through the series, manipulating events from afar and possessing Justine. I have to wonder if there is a distinct seperation being made between the three Walkers: something like Behind is a loner more interested in a good fight, Before is more a psychotic who likes violence and gore and death, and Beside is a subtly manipulative megalomaniac working towards the stated Outsider goal of total omnicide.
Chicago will likely band together to fight off outside supernatural forces from now, as I mentioned earlier. Funny enough, this should ingratiate Harry with the Chicago Police finally, as they've had an in-your-face supernatural invasion occur on their watch. The likes of the Winter Court can probably integrate into Chicago, as long as they're aware there's no preying on Chicago at the same time anymore. As mentioned above, while Marcone is probably pissed off at Harry for his actions at the end of the book, Harry is too useful to him now. If Johnny Marcone is the Baron of Chicago, and he intends to protect Chicago from the supernatural again, having the Wizard of Chicago is also a major deterrent.
Also, fuck Rudolph. I'm not too impressed with how Murphy got killed off.
With her dead, I also wonder if/when Harry will get another lover. I don't count Kim Delaney, so that leaves me at sort-of 5 lovers Harry has had so far - Elaine, Susan, Lash, Luccio, and Murphy. Three of them died in some way sacrificing themselves for Harry, which has really gotta add up for him. The ship has sailed for him and Molly. He might swing back to Elaine, or maybe this thing with Lara will actually move past platonic (extremely, extremely, extremely, EXTREMELY doubtful). Perhaps he'll give up on love for a while. There might be some new female character showing up. I think Ivy is also now 18 or 19, though that may be a little squick for some given Harry knew her since she was 7 and the larger age difference...