This is the driving question of Kingdom Hearts: Chain of Memories, the 2004 Sequel to Squaresoft`s Legendary 2002 Disney/Final Fantasy Crossover game Kingdom Hearts, now Square Enix.

The game begins with Sora, Donald, Goofy & Jiminy Cricket following the King's Letter, carried by Pluto, in a bid to find their missing friends King Mickey & Riku, who are currently time/world displaced thanks to the events of the previous game.

Story: Upon entering the Castle, Sora, Donald & Goofy are stripped of their battle experience, and soon, their memory (Namely Sora).
Sora's salvation is to come at the hands of Namine, an enigmatic, timid girl who knows more than she lets on.
While the Disney Story Segments are more or less the same, the game thrives with it's original story primarily surrounding The Organization, Sora & Namine.

Gameplay: Unlike the PS2 Original, which saw Sora & co hack, smash & blast through an array of foes in low polygonal 3D Battlefields, COM instead becomes a strictly 1v1 affair, where the player's fate is decided by the luck of their draw.
Blindly whacking isn't too effective an option, given limited Card Supply & the need to reload; Thus come Sleights.
In exchange for stocking 3 cards, one can unleash a powerful special attack.
Or they can rely upon Friend Cards.
though, they only come so often, so use your cards wisely!
The System isn't for everyone, considering it's learning curve, but it makes a fun alternative once you get the gist.
Also, Cards aren't just used in battle, but on the Map of every World, also.
You add them up at Doors to open up new areas within said World.
You get Area Cards from winning many battles, oftentimes getting duplicates.
However, if the Battle System isn't your thing, it could be quite a chore.

Kingdom Hearts' score remains fantastical, as it borrows from a wide range of Disney Movies whilst adding quite a few original compositions, each with their own style (For example, Aladdin's Agrabah has a Middle Eastern/Arabic Sound to it, befitting of it's setting).
Whilst much of the music is borrowed from the Original, the songs have been faithfully converted to bless the GBA's Sound font, and to great effect, too.
Standout Songs include ‘‘The 13th Struggle‘‘ (Organization XIII's Battle Theme) & ‘‘Scythe of Petals‘‘ (The Final Boss Theme).

Graphics: Similarly to the original, this game looks wonderful on it's own merits; The FMV cutscenes resemble the High Quality CGI ones used in KH1, while the Sprite work is colorful, clean & compact.
Profile Images even resemble the original game's polygonal Art Style.

The game is fun on a first playthrough, but becomes less so on repeated playthroughs, with the exception of a certain dark rival's story mode.
The story is mostly fun to skim through a few times, but the main draw is usually the gameplay.

Conclusion: Kingdom Hearts: Chain of Memories is a fun, yet unconventional sequel to a beloved game.
I personally recommend playing the GBA Original over it's PS2 Remake, as I feel the former's gameplay system only works so well in a 3D Environment; Take that with a grain of salt.