This is a bad anime. Plain and simple. And that is somewhat surprising, considering that most of its elements usually would make it good. Take a second to look at the scores i gave to its different elements - decent story and characters, good animation and sound.. So why does it turn out so bad? Pacing, execution and the lack of impact after arising interest.
After having everything - as in the budget, characters and the story, i think the error of the creators of this show was to leave it and produce it as is. The anime does a good job at starting, grabbing the viewers interest, and keeping it up until the very end... And then it suddenly ends. That is not to say that i think that the ending was the best episode in the anime, and that I actually would have given it 5/10 instead of a 6, if not for the ending. Aside of the ending though, the anime didn't deliver that much resolution and impact at any point. There are too many characters, and surprisingly they are almost all pretty well written, but the anime simply had no space for them all to fit in with just 12 episodes, so it kept keeping its sense of mystery while switching from one to the other and explaining all those characters, only to run out of time and give its half baked impact, while leaving a lot of things unresolved and unaddressed.
So then, what could have made this anime from the half finished, lighthearted product that it is into a proper, and possibly even really good title? A few things, but things that are pretty easy to do so i'm kind of at a loss why they didn't do it.
1- cut out about half of the characters. Now again, i did say that most of them are pretty interesting and well made, but that doesn't change the fact that they simply do not get enough air time at all, to the point where not including the most insignificant of them would actually help resolve more issues and make the show better by focusing more on the rest.
2- lack of action. There is not a lot of it in the show, and a vast majority of action scenes that ARE present is about the main, or less significant characters seeing, and running from their nanaki. I mean that IS kind of an important thing in the show, but to have so many of those scenes is pretty pointless since they are more or less structurally similar and to get the idea that they are supposed to present, just two or three are more than enough, and repeating them so much, especially for characters that later get thrown away until the show ends is simply a waste of time. So what is the solution? Cut about half of them (goes well with point 1)
3- Lack of tension, fear and actual danger. The tension and fear in the show, while present, feel forced, stupid and out of place, as a lot of people pointed out in different discussions about the anime. The reasons for all of those are usually because of lack of trust, coordination, some suspicion and finally the mental problems of some of the characters (a good example would be everyone's "favorite" Lovepon). Instead, the show should have actually genuinely killed off a character or two, and that goes back to point 2, as in that it would help add action and it would solve the problem of the current point as well, adding fear and tension that would feel more organic.
So then, with all of those changes, the anime would probably be structured like this instead - a bit over half for introduction of the new world and characters as well as the understanding of what's going on, and a bit less than half for the reveal of everything that got shown only at the show's end, and resolving of the problems of all those who wished to leave, along with some aftermath of what happened when they got back, finishing the show with a slight mention of those who stayed behind and how they are coping.
That's enough dreaming though, the show may have been much, much better if made like that, but since it isn't, i'll give a final verdict on what i think of it as it is- its definitely worth a watch, but getting into it the viewer should have no expectations from it according to its tags, but rather expect an interesting world, set of characters and story that ends after its introduction and first chapter instead of going through the whole novel that might have been great
