Well the difficulty level gets harder by 2+ times I think? After you go through your first few playthroughs, so Hard -> Super Hard -> Insane? and then it gets stuck there. Before the Harem route, the only challenging fight is the Four Stooges one, and you just need to keep the enemies at one side and keep on attacking and you can win.
Mia's route is a bitch. I hope that I never have to go through such a horrible route ever again. Absolutely the worst of everything that could happen happened, and the only consolation is that Avatar is saved from 1000 cycle wars.
The only problem I ever faced was when fighting against the Headless Kraken when Taiga is solo charging one last time through the enemy to get to Mia. This boss has insanely good skills and damage; I especially hate his all range ultimate, which hits for at least 1/2 of your HP and has insane amount of range.
Then again, I've played through that part without realizing I could Block. I've been using Parry all the time, right up till Mia fight, so maybe I could've won. Doesn't change the fact that I'm an idiot though. >_>
The Harem route actually provides a decent challenge. I was in a hurry so I just turned down the difficulty for several boss fights that are incredibly hard to win (despite the difficulty reset to joke level) and hurry on the story.
The fights that I couldn't win on Hard include using Lily vs Downy, Seru vs Downy and God Taiga vs Butterfly God. Lily for obvious fucking reasons that Downy said himself: A magic using Swordsman vs a magician = insanely hard fight. At the beginning he wouldn't block as much and you can kill off his HP bar relatively quickly until Green. And that it gets HARD.
His attack patterns begin to have more variation, and when you walk too far away from him he starts using annoying far range SWORD attacks (the irony) and pummel you while you can't see him. Fine. He starts to block 95% of your attacks and you only chance of dealing some actual damage is to predict his attacks and attack exactly before the attack hits you and pray for the best. Like all other enemies on Hard, when they're left with only 1 bar of HP, all damage dealed are reduced (while yours are NOT), which makes it insanely annoying that even with a perfect double Ulti combo (I did it with Lily. That's fucking amazing. Praise me. =3) you hit him like, what, 1/6 of his HP?
Downy also must have some incredible Magic resistance, because he goes down to Physical attacks VERY easily. And now I'm going to talk about the second fight, Seru.
First, you'll going to lose your first fight 100%. Why? Because if you don't know Seru before, his B is a short range jump attack that stabs the enemy downwards from the air, unlike any other melee characters you've played before. It took me one heck of a time trying to get used to this change. Next, His Dash attacks deal SO LITTLE AMOUNT OF DAMAGE it's annoying. With Taiga not only he has insane range on his Punch, he also has a knockback and decent damage and can comboed with Super Punch. Which comes to Seru's 3rd weakness (though this is acceptable), no Ultimate. Usually you'll use your red meters for Ultimates and they'll drain away pretty fast, but with Seru, if you do not at least land one combo on Downy you'll notice that you have way too many red meters and not nearly enough blues to guard. Which means you have to fight Downy at VERY CLOSE melee range, the one thing you DON'T WANT TO DO against him. There's only one time that I've managed to bring him down to literally 1 HP, and I fucked up my last combo and got killed. And then I just switched difficulty because I want to read the story. >_>
God Taiga vs Butterfly God. Honestly, this is another question of who kills who first, and your only chance of winning is to keep. On. Hitting. Parry the thunders, parry the fire rain, somehow deal with the constant CC and keepaway and timestops. If it's only that I have no problems winning this fight, but this boss has one, single game breaking skill that I hate with all my heart.
Mobile Freezing Ice Land Mines. Do you know how annoying that is? One second you're comboing the ass out of the boss and the next moment you're suddenly blast into the air, frozen, with 1/5 of one bar of HP gone. It's not even an ultimate. My bloody Super Punch don't even deal that much damage. This will happen so many times in the game, and it's not like you can dodge it properly when you're busy hitting the boss at melee range.
Oh, and Super Punch is super ineffective against Butterfly God, you're better off using Dive Bomb (you'll be blasted so many times into the air it doesn't matter) and normal AB because they do more damage. The Butterfly God lives up to its name alright: A body so light that you just go through it, dealing light damage, and minimal knockback. Waste of a meter.
After all that ranting about DSJ, now I'm going to talk a little about Fake Azure Arcology.
The plus side. Good voice acting, and three pretty decent heroines: Haruka, Noel, and my favorite Ledi (or Lady). Haruka has the body of a model despite her small breast size, is insanely cool looking, a little innocent for her age and VERY innocent when it comes to her ambitions and dreams (it's like she's high on candy when she talks about Flight). Noel is a cat cyborg with the best character design in the VN, and she's also very cool personality. Ledi is an extremely strong-willed girl, who although is a little insecure because she's a Created Human, had always shown a strong, mature side and never fail to make you smile with hers. Apparently golden hair girls in this series all share the same traits.
The down side. There's a LOT of downside for this one unfortunately. First, the Osanajimi heroine is scary as fuck, almost at the same level as Mia. Spoilers here, but the first thing she did when:
When her boyfriend came back from space after 2 years was to jam a loaded gun at his head. I mean sure, Ledi was fooling around with her now young child body pretending to be Chihirou's 'daughter', but man... WTF girl?
I've had enough of crazy Osanajimi's for a while, seriously, this is literally giving me traumas with all the madness lurking about this route.
The plot, although seemingly promising at first, was pretty bad actually. They had a pretty damn good setting and twist to utilize, but executed it very lamely. Haruka and Akira's route had made a pretty okay impression and I was anticipating a lot more twists to be revealed in the future, but instead there was... how to say? Nothing. Ironically, I can tell that the Osanajimi route was given a LOT of attention and would probably be one of the best routes to read, if I wasn't so freaked out by her attitude and skipped all the lines that has her in it. -_-"
Ledi's route was my favorite, but they really did not add any additional details in her path that wasn't already explained before. I was massively disappointed that even the aerial dogfight in her route wasn't as exciting as it could be. She IS the true heroine of the story, mind you, but the entire VN made it so bloody vague (even with the Grand Epilogue) that I have to check it's SEQUEL to know exactly who's the real heroine, and which route is the true end. It was actually a Noel + Ledi route, but that is not an excuse for poor execution of the storyline.
Its character sprite and sound execution is also weird as hell. One, some of the dialogues really don't match the character sprites they're using. Imagine reading a supposedly sad line with a bright smiley face on the character. Some of the chosen BGMs are extremely vague and they just don't fit any of the themes they're suppose to portray (actually I think those BGMs just suck big time). The experience is just lousy overall.
And finally, the aerial dogfights. I came searching for this VN because it's sequel made me interested, found out that it isn't exactly what I'm looking for, thought that it was fine and read it anyway, and found it disappointing. The dogfights mostly consist of a single CG showing the exterior of the airplane, or the view from inside the cockpit, and nothing else. Plane A has broken Plane B's Visual Sword! CG still shows Plane B completely intact. I mean like wtf, there's absolutely no excitement at all! Man...
When I was playing it's sequel Rebirth: Azure Lost Colony and found myself interested in it's prequel, I was expecting a story about the German colony Stelenglobe, which has a really good setting. First, this colony focuses on pure research and hence has the best technology of the entire world. Second, it is a world where AIs and Cyborgs are created legally, and they also have human rights. Basically they're recognized as an equal to human, and that is really interesting.
So I went in search of its prequel expecting to see a story about the struggle to give AIs human rights + flight, but instead I was treated to a different setting featuring a really disappointing story. Sigh. Oh well.