As someone who has NOT played 358/2 Days or seen the translated cutscenes yet, may I still offer you some words of advice, TerraFTW?
A lot of people on these forums do not like KH2 or found it to be mediocre at best. From the way THOSE discussions tend to go, you would certainly think that the game was epic fail and not a very respectable sequel. I, on the other hand, absolutely loved KH2 when it first came out, and still enjoy playing it to this day. Even if 99% of the people on KHI say that a game sucks, that doesn't mean that you will hate it. There's a very high chance that you will, yes, but it's not guaranteed.
Additionally, I remember hearing about the GBA Chain of Memories while I was playing Kingdom Hearts for the first time, but I thought that a handheld game wouldn't be as good, so I simply skipped it and played KH2. I finally bought it last year (several months before the PS2 version was announced *bangs head against wall*) and loved it. Needless to say, I will never underestimate handheld games again.
If you have a DS, I highly recommend that you listen to Raz and either buy the game or rent it to try it out. It's up to you of course, but isn't it better to try it first instead of not knowing at all?