There is a lot going for this game, but it has a few key missing pieces that I just can't forgive it for.
Pretty much everything in the presentation is great here. Great art style. Very good graphics. Music is good. Voice acting is strong. Story is mostly good (a little more on that later). There really is very little to complain about in that respect.
Game play too is mostly there. You have a very pokemon like development system, with a large variety of creatures, their own moves, own evolutions and so forth. Combat is in real time, making it feel different from pokemon, and is reasonably challenging if you don't power level, but power leveling to just brute force your way by the battles is also an option. There is also some nice nuances to the battle system that add some welcome extra strategy. Out of combat, the alchemy system is reasonably interesting, and the ability to equip your pets and yourself is a nice extra layer.
Unfortunately, it isn't all good. The partner AI is... well broke. You can tell it to do nothing, and it will do things. You can tell it to keep you healed, and it will heal yes, but also cast a bunch of other useless spells. Not only is it broke, it is woefully underdeveloped. I remember back to by Dragon Age Origins review where I complained about he AI there as well, and frankly, I wish I had the barely functional AI of DA:O here, it would be massively better. The only reason this isn't devastating to the game as a whole is you can easily over power everything compensating for this terrible AI.
That's probably the most major issue, but there is a couple of others as well. The first is the excessive hand holding. Every objective is spelled out for you. Every tactic is made plain for you. There is very little in the way of actual thinking going on in the game events. While there are times I thought it was necessary, most the time it just felt excessive. The rest of the issues are really minor I feel they do deserve mention.
The first is the quests. A LOT of the quests are exactly this 'take to person A, find out which piece of heart they are missing, hunt around for person B who has said piece of heart, return to person A and give piece of heart to them'. These are really thin and they make up a good chunk of the quests. The rest of the quests aren't too bad, although if you've done any questing based MMO in your life, they are obviously going to be familiar.
The second issue is the spell book. You are given dozens of spells, but a good chunk of them have 0 use, and even more are only 1 time use. I suppose this is a conflict between story and game play, as the spells are they to indicate there is more to magic than just the stuff you need, but still it feels so cheap to put them in there and not even make good use of them (many of them could have been tossed in just for fun sake even if they served no real purpose).
My last complaint is a very personal one (and I don't knock the game score for this). For me, the story had a disconnect. Much of the story is spent powering up for the big battle with Shadar. This is all fine and dandy story wise. Now every so often they tossed in a scene with another big bad, the White Witch. So, after you deal with Shadar, naturally we quickly move to the White Witch, but she feels so... incomplete. I feel like they had numerous more hours of game planned but had to cut it down and seriously truncated her portion of the game. It is not terrible by any means and it does have all the markings of a complete tale, but for me it just doesn't work. Oh well.
I still very much enjoyed Ni No Kuni, but it was held back. I hope the franchise continues as I can only see good things in its future as all these problems are the type that can be worked out in the future.