I really, really hated Ni no Kuni. The music was good, but a soundtrack that bombastic leaves you fatigued after constantly hearing it over a 50+ hour game. The battle system flat-out didn't work well. The idea is that you can either block, interrupt, or avoid most of the really devastating enemy attacks, but the window between "the attack is being charged" and "the attack is being used" is so small that you can't do anything but guard yourself. Speaking of guarding, the battle interface sucks. So many times when I try to use a familiar's tricks, I had to cancel and guard myself... But can't do it in time, because I have to cycle through all the menu options to find "block". This game really needed "cancel current action (if possible) and guard", or at least better use of the face buttons. There are three defensive options, and only one is good. Each familiar can either "block", "avoid", or "go wild". Block greatly decreases the damage you take. This is the only good one. Avoid doesn't last nearly as long as block, but you negate all damage instead of decreasing it. This would still be a good option, if it worked all the time. Sometimes you take full damage anyways, and I never figured out why sometimes I do and sometimes I don't. I thought it might have something to do with attacks that hit the whole field, but I can sometimes avoid those, so I don't know. Either way, it's unreliable, but a familiar with Avoid is still usable. Then there's "go wild". Instead of blocking, your defensive command becomes "psyche up", which will make you power up and replace your standard physical attack command with "go wild". "Go wild" does nothing except give you a slightly better chance of interrupting enemy tricks with your standard physical attack. It does no extra damage or give any other boost. When you use Go Wild, it reverts back to the normal "attack" command. The problem is, psyche up takes so long to charge you can't possibly use go wild before you get hit by something, making this "defense" command absolutely worthless and unhelpful in literally every situation except if you get very, very lucky and use go wild just as the enemy is starting to charge their attack. Any familiar with Go Wild is absolutely worthless and should be shoved in the Retreat as soon as you catch it.
Swaine is the only likeable character, and that's because he constantly rags on the other idiots in my party. Oliver has no character outside of "goody-goody who's sad about his mom dying", Drippy just sucks, and most of the supporting cast (and Esther) are just annoying.
The plot almost never progresses forward and I could spot almost every twist way before they happened. Most of the "plot" is just Oliver running to various towns undoing Shadar's dirty work while Shadar keeps talking about how amazing and competent he is. The only genuine surprise is that Oliver's mom and Alicia are the same person. I could easily spot that Oliver was Shadar's soulmate. The revelation that Gallus is the Wizard-King's spirit was telegraphed from a mile away. Shadar really trying to protect the world was the only logical explanation for why he didn't just kill Oliver as soon as he started dealing with the Great Sages. Even though they were going for a story book-inspired world, it was done very very poorly. When the plot wasn't being vapid the various locales were clashing with each other. If you want to play a good game that was inspired by fairy tales, play The Last Story.
Really, the only things this game had going for it are the graphics and the sidequest system. The graphics are really nice, but good graphics can't make up for crappy story or gameplay. Not that the graphics are completely free of screw-ups either: The ability "Jumping Jack" lets you jump, but when going down ramps, you're the same height above the ground as you are when you jump on the ground! This really gets on my nerves because Jumping Jack serves no other purpose. Even though it looks like you could jump small gaps with it, you can't. It only exists to eat your sidequest upgrade points and look nice, and it sometimes even fails at looking nice.
I mentioned the sidequests before? Yeah, no complaints here. I absolutely adore the way sidequests are done in this game. Most are relatively short, give good rewards, and give out tokens called "merit stamps". You can cash these merit stamps in for really, really nice character upgrades that help a lot.
This is all off the top of my head. If I sat down and thought about it a little more, I could probably come up with even more things that drove me nuts when playing this turd.