The silver bullet in Jason Schreier's review is: 'it’s all width, no depth'.
The world in this game is pretty appealing but the game part seems like an orgy of useless and confusing systems that only allows for a myriad of numbers to slowly go up. I guess some have that itch that needs to be scratched, but I don't.
The combat system is confusing due to a lack of explanation - but it's pretty fun when you throw all the sums of it's parts together and know what you are doing. The world is gorgeous and the story is up to par so far - albeit a little slow through the first half which is what I was expecting as that is what the reviews all pretty much stated. Second half picks up from what everyone says universally but I haven't seen it yet, I am on chapter 3. With that said, I am still having new tutorials pop up in combat with breaks and when to use certain abilities to the parties advantage. You have to pay attention though and there can be a lot on screen at once which makes it hard to time the 1, 2, 3's with Rex. For instance, one of my ability's drops heal pots on the ground which effect the whole party once you grab them - you want to time these when you see the blue indicator to increase what is called a Art Plus attack, and then subsequent attacks increase your specials at a faster rate. Now with breaks, and that same ability, I can topple a monster to make it not attack for a brief time while pummeling it, but also found out if I have one of my party members use Pandemic, the special combo there creates a large amount of damage. I just had Poppi unleash a ton of damage it's major special. Another one is if I wait long enough, Pyra and Rex will form into one and deal a massive amount of combined damage.
The system is VERY complex and deep, so there is no way there isn't depth to the systems. Not only combat itself with breaks, specials, art plus gains, timing, and other specials from your party members causing other massive combinations, you also have Aux Cores to infuse in your blade which have varying bonuses, a pouch for a passive which is a bonus set on a timer (One for each party member) and they all play together extremely well, and an affinity progression system which can effect field and combat as well.
The problem is, it isn't explained well. And there is no reference material, so you have to go out of game to really understand it, or ask here in the thread.