I started this show back when it first started airing, because I was bored. I've seen most of the big name harem and ecchi series, and figured "I may as well try this.". Mecha isn't really my thing, but the fact that this series is a Mecha isn't even what makes it bad. There may be light spoilers in here, but honestly, this show doesn't even have much of a story to begin with, and I can only imagine one thing that could be spoiled, and it really isn't even that major.
This series really had no overall story. It just had mini-arcs that comprised the whole thing, and then one antagonist that wasn't really explained well at all. The series starts off with the protagonist conveniently falling into a girl's bath. And whadaya know, it's the most important girl in the kingdom! He then has to fight her for some reason to gain entry into a girl's only school to learn how to use his mech. Lets not forget that he is the biggest badass in the kingdom, and singlehandedly overthrew a regime, literally a legend among people. For reasons unknown he has to go to school.
Naturally, their fight gets interrupted, queue the "evil" in the show: the Abyss. They really aren't explained very well either. In the beginning, they seem to have their own free will, since they have no tactics whatsoever, yet later on in the show they exist solely to be used by people who have certain flutes. And there are multiple flutes, which makes it quite easy for people to control them (somehow). Every time one type of enemy gets stale, they get an upgrade, From normal Abyss, to big scary Abyss, to Giant ass fortress.
Also of note, for reasons unknown, I can count on one hand the number of males who could use a "Drag-Ride". Why is it only females? Why is it a female only school? How do the few guys that do know how to use a Drag-Ride learn in the first place when even Lux was given such a negative reaction upon trying to get into the only school ever talked about in the entire show?
I'm no art critic, but I liked the way it looked. It wasn't as good as Phantom World by any stretch, but it was fluid, and looked nice.
The OP is bad. Starts off like it's going to be really intense, then drops into a random electro-pop conglomeration with poorly translated english words thrown in for flavor, like "fight for the sky!". ED is decent, but generic. The Sound effects however are where this show really shines. Every time a character pulls their sword out, my ears have a mini orgasm, and explosions are nice and crisp. A female voices Lux, but honestly, that didn't make the slightest difference to me. In fact, I wouldn't have even noticed if I hadn't read it in another review a while back. Other voice actors are alright, nothing stood out as exceptionally good, or exceptionally bad, so I can't complain.
This show has the worst character cast that I have ever seen. Boring main character, generic tropes for every girl in his harem, etc.
Lux: Main character, has no backbone except to "Protect his friends", never goes on the offensive. His nickname because of this is the "Weakest Undefeated". Is completely clueless about how girls work, and even when he has opportunities right in front of him, he drops them. He lacks confidence in anything but his goal to protect his friends, which makes him lose so many opportunities. He could have been laid many times throughout the season, by any of the people in his harem, yet instead he gets a total of 3 kisses, which aren't dramatic at all, and very anti-climatic, since he freaks out after each one.
Airi: Lux's little sister, because what show would be complete if the main character didn't have a sister that rarely does anything except push him forward in his determination? Has barely any screen time, manages to be condescending in spite of this.
Lisesharte: The princess that he falls into the bathtub with. tsundere, quickly goes full dere in less than a full episode, and then just manages to push herself away from him due to her own stupid decisions, because you can't have a relationship in a harem.
Philphie: the kuudere childhood friend. Eyecandy is pretty much her sole purpose in the show, barely even an interest in his harem. She's too apathetic to care if Lux goes for her or anyone else.
Krulcifer: The only good character in the show. She is the only one you can't always predict, and that is the only redeeming factor characterwise. Still not enough to pull the rating upto a 2.
Those are the only characters I even know the name of. There is a great deal more of them, and none of them are really of any consequence. A brown haired chick that serves no purpose other than pushing the members of his harem closer to him. A black haired girl who is emotionless. I know I'm forgetting characters, but clearly they weren't important enough to remember anyways. Most of them serve a single purpose as a plot device, and the only characters you get a backstory for are Krulcifer and Philpie.
This show was one of those where you watch it, in full knowledge of exactly everything that is going to happen before it actually does. It is nothing if not predictable.
Unless you're trying to get someone introduced to all of the common harem-genre antics, I would not recommend this show to anyone. I was quite looking forward to just getting it over with at the end. I could recommend many other shows that do harem better than this, and even Infinite:Stratos did harem better than this. It's no good as an ecchi, since the only ecchi is a bath scene at the very beginning, a 5 second scene in the second episode, one back massage with Celes and then Phi's boobs constitute the rest of the ecchi throughout the rest of the show. It's not good as an action, because there is too much drama involved with personal relationships.
TL;DR Avoid this show unless you are out of any other show you could possibly think of, or if you are introducing your friends to the nuances of weak-character harems.