All I can grasp about Re:CoM is that they took the GBA version and slapped the PS2 graphics on there. If they made no changes to the gameplay during the port, then I could agree with reviews that it can be a tedious and unforgiving game. Here is what I experienced with the GBA version...
I managed to get most of the way through the first part of the game on GBA (oh yeah, there's two parts) but I was hindered by a boss battle. In most RPG's one fixes this problem by going around beating up monsters for a few hours until much level-upage occurs and beating the boss becomes cake.
The problem I had (again with the GBA version, if they fixed this in RE I'd cry with joy) is that the monsters in CoM do not respawn. Once you've worked through an area, they're gone and gone forever. This makes grinding a few levels pretty impossible (unless you use a card and make a new area and blah blah blah...)
The other thing was that some doors require a certain card combination in order to open and (duh-duh-duh-Duuuuh) you guessed it, these cards drop from monsters. I was hit with a similar problem of lack of monsters and extremely back luck with card drops, and it was excruciatingly annoying.
I'd have loved it if RE: CoM chucked the whole card schtick, but they clung to it, of course... It's not that it makes it that much more complicated (eventually you sit down with a FAQ sheet and learn how to arrange your cards so you're not flipping through them too much during battle) but it certainly stopped me from running out and buying RE:CoM like I did all the other Kingdom Hearts games. (And why don't they release the "Final Mix" versions of the other games in America? That is a separate rant...)
At least it's prettier than the GBA version...?