It's a fascinating idea and one of the highest-profile anime series of 2017, attracting a ton of attention and criticism. It's pretty cool. I don't think anyone thought it was perfect, including me. However I'm prepared to cut it a lot of slack and I'd still recommend it.
It's set in a world that's being invaded by fictional characters. It's a very low-key invasion, mind you. There's a Military Uniform Princess who's importing fictional heroes one by one and trying to recruit them. (She only succeeds half the time, so we soon have two opposing sides.) What's interesting is that the invaders learn that they're fictional, sometimes start reading their own (or other people's) stories and usually start looking for their creators. What would you think if you learned that you'd been born into a war-torn hellworld and your friends all killed purely for the sake of entertainment?
There's lots of wrinkly exploration of the ideas. Creations meet their creators. There's a teenager who wants to be a creator, but in fact was just another internet wannabe with some disturbing character notes that are saying very very dark things about internet fandom. (Seriously, that chap will make you squirm when he's telling the story of Suicide Girl. What's worst about it is that he's ostensibly the protagonist and he feels as bad about all this as anyone.) There's examination of the symbiosis between creator and audience. Who has the power, really? The creator, or the readers who may or may not accept the latest narrative? This even ends up becoming a major story element, because manipulating stories to draw power from them is what's fuelling both the goodies and the baddies.
There's self-aware material that in any other story would be breaking the fourth wall, but here isn't (except maybe the recap episode). "The quality is getting worse." "The industry is in a crisis." Meteora suggests that the creators add bikini scenes and fanservice to increase their audience figures, shortly before the show does exactly that in ep.16.
You could even read it as a loose deconstruction of religion. The creators are often called gods. They are, literally, the creators of worlds. However they're also unheroic, mundane and sometimes childish. If someone like that was your god, you'd turn to atheism or deicide. Don't think the latter doesn't happen, incidentally.
Then you have the creations. They're interesting to start with, thanks to the headspin of discovering that they're fictional. (Their observations about our world are interesting, e.g. we have a greater information density. The tastes of food and drink are deeper.) However they're still larger-than-life fictional heroes (or villains), which you'd think might be in danger of making them predictable. Aliceteria is a terrifyingly honourable knight who'd never: (a) back down from a fight, (b) even think a dishonest thought or (c) take less than about six or seven episodes to change her mind about anything. Strong, yes. Clever, no. However they're capable of becoming more complicated people in our messier, more ambiguous world. Ironically, the strongest example of this is the purest, most simple-minded cast member: Mamika Kirameki, the magical girl heroine of a kiddie show. She believes in goodness and the power of love. She shoots giant hearts. She thinks that if you defeat an enemy, they'll become your friend. However she's also the first creation to realise how she's changing and to try to think it through.
(I love Mamika. She's brilliant and she can make any episode more fun.)
All this is great. Why might someone be disappointed in this show?
1. I WANTED MORE FIGHTS!!!
Since it's basically a big crossover with both sides including both heroes and villains, you might be looking forward to battles and cool action scenes. If that's what you wanted, then you'll think the series starts slowly and has a really disappointing ending.
I'm not in this camp, personally, but I do think it could have afforded to have a bit more violence here and there. Blitz Talker, for instance, is a tough old cop with a gun and on the side of the baddies. That's a good start, but I think the character would have had more punch if he'd had a body count. The whole point of the character is that he'd shoot anyone in a heartbeat, so let's have him actually shoot some people and get us more scared of him!
(It's not even as if the show's bloodless. Important characters can get killed. Magane in particular is a psychotic evil bitch who'll murder a shopkeeper because she's bored. She starts out as a random serial killer, but quickly figures things out and basically turns into Satan. She's a sexy schoolgirl from the neck down, but she's also got fangs, a creepy face and a subtle hollowness in her apparent happy chirpiness.)
2. I WANTED FEWER FIGHTS!!!
Personally, I thought there was too much fighting. It's as if the show has two modes: (a) really interesting material about the nature of storytelling, or (b) creations battling each other. The show's last third in particular got a bit repetitive, although fortunately they turn that around for an outstanding ending. Personally I see the last episode as positive, by the way, although also of course emotional. I particularly liked the final reminders of fallen comrades, although I did note that we've been left to fill in the blanks with a certain bad person.
I don't think the plotting made best use of the creations, to be honest. I liked them all as people, by the way. It's because they're such engaging, lively characters that I'd have liked to see them given more imaginative story roles. Occasionally one of them might carve a different plot niche for themselves, but mostly they're just there to fight. That doesn't affect their likeability, comedy value or how cool they are, but it's true. (Another of my favourite creations was Hikayu Hoshikawa, who's from a hugely inappropriate genre and is mortified to learn what she's famous for. My heart bleeds for her, but she's also very funny.)
Maybe the show's too long? You could probably lose a quarter of its episodes with little effect except to speed up the storyline and reduce repetition in the birdcage battle and the invincible baddie's actions.
Despite all these comments, though, I liked this show a lot and I was always gung-ho for watching more of it. I can see things it could have done differently, but I think it's got interesting things to say about its attention-grabbing premise. It's thoughtful, yet also a multi-genre battle crossover. It also has lots of nice character work, with for instance the mirrored insecurities of the creators (capable of admiring each other's talents a bit too much) and the way two unlikely people come to understand each other in ep.18. I could almost imagine them having a relationship, although the "spree killer" thing would be a problem. It's definitely one of the most interesting anime of 2017.
"If I can speak for the animation staff, this character was designed just to make their jobs difficult."