Just wondering of all the games released, Kingdom Hearts Ii is considered the biggest game in terms of content and story? --- Of all the gin joints in all the towns in all the world, she walks into mine - Humphrey Bogart - Casablanca
KH1 is generally thought to have the better story (more 'Disney magic'), whereas KH2's plot is fairly nonsensical. In terms of gameplay, the rerelease of KH2 (KH2: Final Mix+) is regarded as having the best gameplay in the series, and probably the most content in terms of things to fight.
For "biggest", there are only two console games in the series: KH and KH2.
The others, while involving and enjoyable to one degree or another, were designed for handheld devices -- Coded, for a mobile phone -- with limited capabilities. Story and content suffer under those restrictions. "Bigger" is simply beyond the capabilities of those devices. --- Guides and other contributions: http://www.esque.com/slr/gamefaqs/ FFX, FFXII, KH, KH Re:CoM, KH2, Okage: Shadow King, Secret Agent Clank
But alot of the canon stiory of the series is introduced in these games, like origin of xenoxort. The X-blade etc! --- Of all the gin joints in all the towns in all the world, she walks into mine - Humphrey Bogart - Casablanca
All of which are off-topic or spoiler turf on this board. If you wanna talk about those things, the latest game's board is a far better choice than here.
Why bother? Because "release order" is most often recommended for players new to the series. So a sincere thanks on the behalf of those players.
As far as...
the canon stiory of the series
Study it, how it has changed at each new introduction. Historically the continuing story includes plenty of evidence that what was told will be changed in a later game. Not the particulars themselves.
However "important" -- not the same as "big", BTW -- something may seem to any given player today, it can and probably will change tomorrow. Expecting it not to change or not to have its importance downplayed later is akin to tilting at windmills.
Like the proverbial spoon, there is no KH series canon, not one that's entirely sacrosanct anyway. --- Guides and other contributions: http://www.esque.com/slr/gamefaqs/ FFX, FFXII, KH, KH Re:CoM, KH2, Okage: Shadow King, Secret Agent Clank