It's a mess. It's almost amazing to see what a total pig's ear it makes of conveying some fascinating ideas. I sort of like it anyway, but that's mostly for its potential and setting. It's based on a visual novel, you see, which will have had lots of different gameplay routes and far more storytelling space. The impression I get is that this is a unique, mind-blowing story that would probably rock your world if you spent 100 hours exploring the visual novel. There's room for that in a computer game. Trying to appreciate the story through this anime, though, is like watching someone smash a stained glass window and then showing you their favourite bits of it. Here's a Subjective Plot Synopsis for the anime:
Ep.1 - we visit a steampunk world-ship with three girls and lots of pretty, charming boys who all look the same except for hair colour. I struggled to tell the difference between the latter almost throughout, to be honest. (It's based on an otome game, which means you play a heroine and will get to romance the boy of your choice. Each of the three potential game heroines has three romantic options, so there are nine boys.) Senri I could recognise because he's a grumpy, whiny wet blanket. (This is good. I like being able to recognise people.) Of the others... well, they're variations on a single mould, really. Same facial features, same game function, different personality traits from a standard list of them.
Eps.2-7 - relationship stuff rather than plot. People emote. You could skip most of this and not notice, except for probably being very confused because it's a very confusing setting. The only important episode is ep.5, which is a dream where the three heroines become Cinderella, Snow White and Little Red Riding Hood. Seriously, that's the memorable one. It's a shared dream that everyone remembers afterwards, which actually has goals and dramatic momentum.
Ep.8 - explanations, which are mental. Holy flaming cow.
Eps.9-10 - WHOAH, PLOT! Where'd that come from? There are actually some fascinating ideas in here and I'd love to see a story that explored them. (This is not that story, although the visual novel might be.) However it says everything about this series that even the recap episode is confusing.
Ep.11 - includes my favourite bit, but unfortunately this involves a character who's not involved in any of those romantic routes. Sorata Suzuhara has barely existed in the story so far. He'd mostly seemed like a walk-on extra who's there mostly for the sake of yet more story weirdness. I'm going to be generous and assume that he works better in the visual novel. This is a fairly gobsmacking episode, but unfortunately some of that is me going "WHAT THE HELL AM I SUPPOSED TO BE THINKING JUST HAPPENED?" Something apocalyptic happens, but it doesn't make sense if you assume that it's what we're presumably supposed to think it is.
Ep.12 - aha, an anti-explanation! However at least they acknowledge that thingy wasn't thingy. I approve of the story's moral and the tone feels appropriate, but it seems that one can stop a war by destroying one munitions factory.
There's a fascinating story here. It involves 1919, 2016, 2056, 2067, 8075, two thousand years ago, truly mental time ideas, reincarnation, super-cool steampunk guns, psychic superpowers, a dream world, World War Four, a glowing ghost girl, a schoolboy from the future, memory-erasing and a beautifully intricate spaceship that you could be forgiven for deciding must be operated by doing the gardening or something. Does it have AI, maybe? I think our heroes are flying around the world on a sort of steampunk air cruise, but don't hold me to that. At one point I think they stop off to go shopping in Turkey. You can still imagine a good story from the bits that have made it into the anime episodes, or else you could give up and buy the computer game.
There are lots of boys you'll struggle to tell apart, plus three underwritten heroines who don't get enough to do. The boys do have different personalities, but they're less distinctive than, say, the parody boys in Cute High Earth Defense Club Love!. As for the girls, Shiranui (pale purple hair) is emotionless, Mikoto (black hair) is cold and Koharu (pink hair) doesn't have an identity. At least Shiranui and Mikoto seem like people, but Koharu might as well be a walking script note marked "generic loving heroine". I didn't really care about the romances, to be honest, but the show puts lots of effort into them and they have some interesting aspects. Shiranui's pretty messed up and Mikoto's relationship's not exactly calm either.
I think the lack of backstory hurts the characterisation. The most intriguing thing about ep.1 for me was this mysterious, paradoxical world in all its steampunk SF strangeness, but the corollary of mystery is a lack of information. We don't know much about the main characters. Sometimes even they don't know much about themselves. They're just there. They might as well have sprung from a void. There are some childhood flashbacks that are crucial for the relationships, but the show can't say too much because it's saving up its world's backstory for ep.8. Thus both the boys and girls are in danger of coming across as generic types in a vacuum.
I wouldn't recommend this, to be honest. It's not bad because it's a reverse harem show, but rather because it's crushing an amazing world, backstory and concepts in the process of using it as little more than a backdrop for some relationship stories that I'd rate as "not bad". Most of the characters are a bit anonymous, but the stories being told with them are okay. Shiranui's was my favourite. The show's world is undeniably compelling and beautiful, though, and I'd go apeshit if someone did a really ambitious remake of this. For now, though, stick with the computer game.