Just watched the finale of ID:Invaded this morning. To be honest it was a little underwhelming. The final battle with Hayaseura/John Walker was cool, but as a character he didn't really get fleshed out enough to be a compelling villain. By the end it wasn't even clear what his goals were, or why he did everything he did. What was his endgame in linking himself to the IdWells of every serial killer in the world? I presume he was creating serial killers as "test cases" for the Mizuhanome system to prove its efficacy, but I don't get how releasing Kiki and turning the Kura facility into a giant IdWell fit in with that. I just wish his motives had been a little more clearly spelled out.
The resolution of Kiki's plotline was also morally pretty iffy. So Momoki refuses to kill her to put an end to her suffering because that'd be wrong, but apparently stuffing her into a machine to experience being brutally murdered by serial killers over and over again is A-Okay? I don't really buy that she's okay with it either. This isn't a typical "life can be painful but it's still worth living" Aesop, Kiki's "life" in the Mizuhanome consists of literal endless suffering, with only the faint hope that she might be saved someday. Even if she's resigned to it by the end, pretty much nobody- much less a traumatized teenage girl- could find happiness or serenity in that.
If the Kura squad keeps using the Mizuhanome even while knowing its true nature they're really not any better than John Walker. Narihisago is seemingly the only one locked out of the loop at the end that Kiki is still alive and powering the Mizuhanome (since he was stuck in the Well while shit was going down IRL), so I can't help but wonder how he'd react if he found out. Given how determined he was to save Kiki back in her IdWell, I can't imagine he'd take it well...
Despite those complaints I still enjoyed the episode. There were some awesome moments, like Hondoumachi literally bodyslamming Hayaseura with a shark (honestly I had a giant grin on my face during that scene) and the way Hayaseura got ultimately defeated was pretty cathartic. He hoped for a grandiose martyr's death at Sakaido's hands, instead he gets ignominiously tricked and forced to live out the full consequences of his crimes in Kiki's IdWell. For a man with delusions of godhood who thought he could escape all the consequences of his crimes by dying in the IdWell, there's no more fitting fate than to be arrested and tried like an ordinary criminal.
As a whole this was a fun psychological thriller show with some likeable characters and a relatively unique sci-fi premise, which is really all I asked for. The animation and background art in the IdWell sequences was consistently imaginative and occasionally jawdropping (Fukuda's IdWell in the first two episodes is still one of the most visually creative setpieces this season, I reckon), so I'd recommend the show for just that reason.
But I do think it could've been better if some of the characters were more fleshed out. Hayaseura is an obvious one, but Hondoumachi also has some wasted potential. There were ominous hints throughout the early episodes that she secretly enjoyed killing and was in danger of becoming a serial killer too if she wasn't careful, but that never really went anywhere. After she got transferred to the Kura squad she was a pretty straightforward heroine, with her supposed bloodlust never brought up again. So yeah. It was a good show, but at times felt more like a vehicle for the various sci-fi and psychological concepts at work than a fully fleshed out narrative.
Also, if anyone else finished the show and is still hungry for more, there's a manga of ID:Invaded running currently. It's called ID:Invaded #BRAKE BROKEN and features an original case starring Sakaido in an IdWell where he's stuck in an out-of-control car. Given the anime ends with Sakaido and Hondoumachi continuing to solve cases as Brilliant Detectives, it's possibly even meant as a sequel. I might check it out sometime soon...