Level design in KH2 is trash unless you're a fan of FF13's corridors. On the other hand, the combat is arguably one of the best in ARPGs history.
Story is well... I don't even know where to begin. If you're planning on skipping CoM, then you're probably going to hate the beginning because nothing will make sense. Actually, I take that back, nothing makes sense in KH2 unless you're really deep into the lore of the series and analyzed the hell out of the previous two games, and that only gives you some background information to work with so you can make informed predictions at where things may be going.
Other than that, prepare to be lost throughout the entire game.
Watching chain of memories on youtube. Read the Ansem reports.
I grasp the concept of nobody and somebody and that the organizations consists of nobodies?
We'll see how I feel about KH2. I'm mostly playing through the series because I think KH3 could be an excellent game and I want to be able to understand at least some of it when it comes out. Also I look forward to BBS because I played it on PSP even though I didnt understand the story I remember I very much enjoyed playing it, never finished it though.