I've played and beaten all of them except Unchained X :p
Yes I'm a diehard fan.
I'm still in the middle of union cross. Level 206 chapter 127
Kingdom Hearts is just one of those games that's so easy to fall in love with because it's so fun, interesting and does SO much more with the idea of combining Disney and Final Fantasy together in a game series. Fun combat, lovable characters, plenty of story and lore to keep the story players interested even if it gets ridiculously convoluted at times and it's SUPER colourful! I love colourful games, even in the days of the PS2 era I felt a lot of games were washed out with muted colour palettes so seeing a game as vibrant as Kingdom Hearts certainly caught my attention when I was younger.
Not only that, the best action-RPG that I will play besides Tales of Symphonia, and Secret of Mana and some others that relates to it's similar gameplay! ^_^