10 hours in on Critical Mode with Terra and having a blast. The battle system in this game is EASILY the best in the series. Leveling up commands is such a breeze and melding them together becomes all the more addicting because of how rewarding the combat is. I know KHII kind had a similar Journal that recorded everything, but I still love the feature in general. I also love the sticker collection idea, small stuff like that is always nice to see and I didn't expect there to be anything like that in the game.
My only complaint so far, as I believe a few here mentioned already, is the lack of life and characters in each world. I only played through the original KH in its entirety so I don't remember if the others were like this too, but it seems like the whole series has this "empty" world feeling. I am also not really a Disney guy so I don't know what characters you could really add to each world to give them more life, but it really does feel odd that the only people you meet really in each world are those who have something to do with the main character/plot.
Also, the world design is pretty boring, but again, I remember the original KH feeling the same way. There are no puzzles or environment traps or any interesting stage design ideas. It's really just rooms and corridors filled with enemy spawns and events. I think the series could really use a new stage design mentality. I mean, they are working with famous worlds and characters so you think they would be more inspired to create interesting stages.
Deep Space felt like the best effort I have seen so far and even then it's pretty boring. There could have been some cool gravity scenarios or something instead of some blocks that float and platforms that rise and fall.