Basically everything you've been told about Kingdom Hearts by its detractors is wrong (and I say that as a detractor). Every Kingdom Hearts game has the same problem- a huge portion of the runtime is devoted to running through an empty, dull, flat environment themed after a Disney movie while being subjected to what essentially amounts to a Wikipedia plot synopsis of that same movie. It's shockingly dull. Kingdom Hearts is at its best when it's just being corny (and eventually convoluted) Final Fantasy but with Mickey Mouse running around in there.

KH2 is the only game in the series that's actually good enough to justify the massive time-waste of boring plot summary and dull world design (seriously, every original environment- twilight town, hollow bastion, etc. looks amazing and every Disney movie world just looks like a generic video game environment). The gameplay is.. fine. It has high highs (many of the bossfights are excellent, the Final Mix version's additional fights are some of the best gameplay in the series) but low lows with plenty of dull combat against generic enemies due to Sora having a very limited moveset at any given time (lots of options, but you can't use many at once). The real draw is the story, which (when it's not Disney stuff) oscillates wildly between being astoundingly great (the prologue/opening sequence of KH2 is just straight up excellent story telling) and ridiculous unintentional comedy.