I finished Kingdom Hearts: 358/2 Days earlier.
From a gameplay standpoint, I believe it's by far the best game in the series. From a technical standpoint, it's definitely one of the best DS games I've ever seen or heard - they used almost every bit of that 256MB DS card, whether it was for the music (higher-quality than most other DS games, since they didn't have to compress it as much as with a 128MB card), graphics (though the DS really doesn't need to be doing 3D stuff like this when it does fully-sprite-based graphics so much better), or the more than half an hour of FMVs. From a story standpoint? Well, I've seen worse. It's definitely entertaining enough that I stuck through with it to the end, and it does a decent enough job of bridging the rest of the gap between the two console games. A lot of it is absolutely ridiculous, though, and too many of the characters are still completely unlikeable (including the character that only appears in this game).
It seems like there were some missed opportunities and some irritating quirks in the gameplay as well. In one mission, the player's level is halved due to Roxas "having an off day." This idea could've been expanded upon - there could've been missions where he's having a really good day, resulting in, say, 20% more experience, or extra casts of all of his spells. There also could've been more in the way of randomness with items, and the cap on items you can carry back with you from a mission was too low in a few cases later on where enemies would drop item after item in a mission that also had eight treasure chests. Also, a word of advice: do not equip Glide and Float at the same time. Float overrides Glide and, because it's set to the jump button, makes Glide very difficult to use. Finally, it seemed weird that I could ignore the Aero and Blizzard lines of spells completely throughout the second half of the game with no negative repercussions whatsoever - don't punish the player for not having all of the spells equipped all the time, of course, but perhaps those six spells could've been tweaked a bit to be more useful. Maybe they're more useful in multiplayer?
Also: Donald, Goofy, and Mickey are playable characters (in mission mode only - you're stuck with Roxas for the whole of the story mode), and Donald and Mickey's utter lack of height means they're very useful in a good number of situations (Mickey moreso because he isn't useless in melee like Donald is). This is very awesome.