358/2 Days is actually a pretty great game. The graphics are fantastic for a DS game, and the combat is a direct copy of the main games. The only drawback is that the story is a little slow, and things get a tad boring sometimes. You spend most of your time revisiting worlds you've already been to, as if you hadn't been to them before. Sometimes you're just fighting enemies, sometimes you're doing "recon," which is retarded because, as I said, anybody who's played the other games knows what the hell Agrabah is.
And yeah, I heard Chain of Memories was awful, but the PS2 remake looks (graphically) just like the main games and all the ratings say it's pretty decent.