1. Kingdom Hearts - Yes, I'm a Kingdom Hearts purist, and I'm god damn proud of it. Say Kingdom Hearts, and I'll assume you mean the first one. This game formed my entire childhood, and it deserves to have a god damn statue memorialized to it in Walt Disney World it's so criminally good sometimes. Is the gameplay clunky sometimes? Sure. Is the magic kind of pointless sometimes? Sure. Is the dialogue cheesy occasionally? Occasionally. Does the story kick ass? YES. Overall, this will always be my favorite title to my heart, no matter what other more fun or well-designed Kingdom Hearts game comes in its way.
2. Kingdom Hearts Chain of Memories - I know this is a VERY unpopular opinion, but Chain of Memories is freaking awesome. Great gameplay, a fantastic, gripping story with so much more character development than I think the rest of the series, a kick-ass set of villains that are completely unforgettable, and overall a great opener to its successor, Kingdom Hearts II. Also, Repliku's death is absolutely heartbreaking.
3. Kingdom Hearts 0.2 Birth by Sleep - A Fragmentary Passage- - This game was very short, so I guess it didn't really have too long to disappoint me I guess. The visuals, gameplay, and level designs were absolutely masterful, with the series going back to its platformer roots and succeeding, the areas being made wide and expansive with minimal loading screens, and the situational commands option being a much desired replacement to the reaction command element of Kingdom Hearts II. The story was short yet satisfying, and it led to Kingdom Hearts III relatively well. We'll just see how it works out when Kingdom Hearts III comes out.
4. Kingdom Hearts 3D Dream Drop Distance - Overall, the one thing that saves this title is the excellent gameplay and huge, expansive area maps as opposed to the original numbered titles. The voice acting can be hokey and off sometimes, sure, and Haley Joel Osment certainly didn't do his best job with Sora especially, but the beautiful, gorgeous landscapes and teeth-gritting, forward-moving plot certainly does its job: wanting us to play Kingdom Hearts III BADLY.
5. Kingdom Hearts II Final Mix - Face it, guys: if it weren't for the Final Mix version we got in 2.5, this would be at the bottom of my list. The story towards the end is great, but everything from the second Sora wakes up to the battle of 1000 heartless is absolute trash. Pacing, what's that?! Did the developers just forget about the nobodies on the first trip around the worlds? I can't remember a single instance of a nobody (other than Xaldin) appearing in the Disney worlds until post-Battle of 1000 Heartless. This pacing issue is absolutely awful, and, I've got to say, I used to despise this game. The level design is linear, I swear it feels like I turned on a cheat code for invincibility in the original version I was so overpowered as Sora, and the Disney worlds were so incredibly phoned in. Also, I don't care what people say, Land of Dragons or whatever SUCKS. This game thought that all they had to do to make the game more difficult was to throw in cheap, practically invincible enemies to piss you off every once in a while, such as the assault riders or the hot rods, and then occasionally make a cheap, practically unbeatable boss to stand in your way, like Xaldin or Demyx, and that's just not fun. Good thing the cavern of remembrance was chock full of difficult enemies and platforming to help sift through the trash, and all of the extra bosses, as well as the extra fight with Roxas, made the gameplay that much more enjoyable. I don't hate Kingdom Hearts II, but it gets way too much praise for what it is.
6. Kingdom Hearts Re:Coded - I love this game, don't get me wrong. The gameplay is great, the voice acting is really good with dialogue that's endearing and well-written, and the villains, while thoroughly forgettable, are threatening and fun nevertheless. I remember walking away really enjoying Data Sora's character, and having fun fighting, but for some reason I can't justify this higher on the list. Ah, well, just know that I mean that I love this game regardless.
7. Kingdom Hearts Unchained X - This one benefits from a great story, a free-to-play base that doesn't make my wallet cry (that's VERY important), and gameplay that's... alright. I like Unchained X, don't get me wrong, but not that much. And I like the gameplay fine, I guess, but not that much. It's all kind of meh to me, I'm considering quitting the game and just watching the cutscenes online by this point. it's just not that interesting.
8. Kingdom Hearts X Back Cover - I like Back Cover fine, don't get me wrong, but I don't love it either. It's a good story with generally good voice acting, but it's certainly not fantastic, and the ending suggests an extra 30-40 minutes that are absent from the actual movie. Overall, this movie just leaves a lot to be desired.
9. Kingdom Hearts Birth by Sleep - Birth by Sleep embodies everything wrong with this series. Terrible voice acting, completely meaningless Disney worlds, useless forgettable party members that you can't even keep when you revisit the world, and one single ability that pretty much wins every fight in a couple of hits. The choice to split the story up into 3 playable characters is all fine and good, except the timeline is contradictory and nonsensical, the voice acting for the characters can be really, really bland ("the weirdest brothers" and any line out of Terra's mouth are examples), and it all leads up to a kick-ass ending that I'd recommend anyone playing the game to wait for. i'm serious, the ending is great. It's just a shame that everything up to the ending sucked really, really hard. Also, the secret episode kicks ass, if that wasn't already a given.
10. Don't mean to copy launchpad here, but Days really, really sucks
EDIT: Now that I think about it, I guess Kingdom Hearts II could lay anywhere in between chain of memories or Dream Drop Distance. I wasn't feeling well yesterday, so I was especially salty towards it, but in reality there's a lot to like about this game. The voice acting is great, the new characters for the most part are all welcome to the series, the fights kick ass, and the gummi ship missions are much better than the original installment where building a gummi ship felt like playing a game of operation without the tweezers. That and the story towards the end is really, really good, it's just a shame that it wasn't paced nearly well enough to pull it off entirely. The Final Mix version is still what saves this game for me, though.