Wow, and ALL those games/cinematics are included in these two packages?

That's at least 200 hours of (fine) gameplay without side quests and grinding.

Oh ignorance, such blissful ignorance...

Or did i miss something? At the end kf KH2 wasnt there a teaser for KH3? that whole keyblade graveyard thing. 

Unless that turned out not to be a trailer of KH3 at all.... either way, KH3 has been a looooooong time coming. 

The secret ending of KH 2 was in reference of Birth By Sleep.But I think many people misunderstood at the time, so it is understandable.

Why do you think so? Besides the fact that it takes place earlier chronologically, which is not a proper reason in itself. Star Wars Episode 1 was meant to be seen after Episode 6. You're not supposed to know that Luke's father is alive when Ben tells him that his father is dead in Epi 4, and that revelation was meant to be a big plot twist, etc.

As for Kingdom Hearts, I disagree because there are similar issues there if you start with BBS. Like why Roxas looks the way he does. The fact that the Organization 13 members used to be normal humans who looked the same way. The mystery of Xemnas, and his cryptic message to a blue suit of armor, calling it friend, etc. These are meant to be mysteries, or things you're supposed to ponder over. Not have all the answers instantly, before you're supposed to get them.
And when Aqua hears Sora's name in the ending and cries, and you see scenes of verious people from Sora's life, you're supposed to know what those encounters he's had represents, and what he has gone through up until that point. But since you barely even know who Sora is if you start with BBS, the scene won't have the impact it's intended to have.
Then you also see a scene with Sora, Riku and Kairi reunited in the end, which makes absolutely no sense if you haven't finished KH 2 already.

I can go on. But BBS was clearly written to be experienced at a later point in the series. Playing it first will ruin a lot of scenes in it, and spoil things you're not meant to know yet in the other games when you play them afterwards.

Well at least the person who asked the question doesn't need to wait years for most of those mysteries to be revealed, like those of us who started at the beginning did, and can just play them all back to back, with the exception of KH 3.

And yeah, I can see how you'd get something positive out of knowing Anikin's story before seeing Vader. I guess the question is what the trade off becomes. If you gain one thing, at the cost of losing two other things in the process for example. That's one reason I tend to go with the order in which the story is presented most of the time, because there are intentions from the writer that may be lost otherwise.
But I also like that way of telling a story, so I don't inherently have a problem with it. I like it when stories become a bit convoluted, and exploring the past after certain themes are already established can be a very interesting way of doing that. A lot of stories do this, in some way or form. Whether it's just a short scene/flashback of an event from the past, revealing some truth in the present, or something more.

I will say that Kingdom Hearts story has become even more convoluted than I would have liked, in the sense that it's hard to piece together all the chain of events that lead up to KH3. But I don't think BBS's placement in the order is particularly related to that, (Dream Drop Distance is a big culprit though, and it taking place in the future didn't help the matter either because it introduced the confusing concept time travel) because many of the revelations in BBS were revelations to mysteries we never knew existed before playing BBS. For example, we didn't know that there was a special reason for why Roxas looked the way he did until BBS was made. Although it's unusual that a Nobody looks so different from their host, Namine also looked different from Kairi, so it wasn't implied that Roxas looked that way because Sora has the heart of someone else (Ventus) inside of him.
Another thing is the encounter between Terra and young Riku, which could explain some things about Riku's connecion with the darkness, and why Ansem (Xemnas' heartless) was drawn to him.
Of course there are also revelations to some mysteries from previous games here, such as learning more about the story of Xemnas and Ansem The Wise, which started being introduced in KH2. But that would have been revealed in the next game anyway, if it hadn't in BBS.
The difference is that if it would have been reveal in a game that lies ahead of KH2 chronologically, it would have been through a limited cutscene of a flashback. Which can make it harder to understamd. But instead we got a much more proper and fleshed out explanation thanks to BBS taking place around that time, and a whole story being built around it. That's a good thing, imo.

I think what really started convoluting the story was the introduction of Xehanort, and to a degree Terra, Aqua and Ventus. But at what time you experience their story doesn't help sorting out the spider web that is the plot, because their stories get integrated into various different points of the story regardless. Especially Xehanort, who can time travel.

BBS taking place in the past helps integrate the stories of these characters in a much more fleshed out way than if it was all summed up in a few flashbacks in KH3 or KH DDD. I'm not sure what exactly it was you had a problem with though? You mentioned Roxas and Ventus, but as I mentioned above, there was no mystery implied to Roxas appearance until BBS came out. Of course if you saw a promotional image of Ventus a year or so before the game came out, the wait to find out what it means would be long.
But one thing that's important to think about when recommending in which order a story should be consumed is if they may miss out on things intended by the writer by going at it in a different order. Besides the things I mentioned before, there's also that when we first see Aqua and co, the concept of a keyblade is presumed to be understood by the player already. As is the concept of a Heartless, etc.
That's why it's also important to make it clear to them in what order the games were released, unless it's obvious from the way the games are titled. Because they may have a preferance already, but might still want some suggestions. For example if a game has little to no relation to the other games in the series.