Kingdom Hearts 3 will release toward the end of January, so now is the time players are looking into the game's various special editions and pre-order bonuses. Hopefully this helps, either way, happy to help (or hurt, considering how long this was).Square Enix is finally taking players back to the world of Kingdom Hearts some 13 years after the previous numbered release.
It can be a little daunting, but I finished all of them before 3 in a few months tops (which for 6 games and 3 movies was incredibly hard to do). It's the best bang for your buck imo I've ever seen in a game bundle, I've logged in 300+ hours over all of the games combined. ALL of that is included in one package in The Story So Far where you can play it either chronologically or whatever order you choose. The last part was the 3DS game called Dream Drop Distance (awful name simply so they could call it KH 3D(s) but the gameplay is actually some of the best in the series, and 2.8 which is like a 2 hour prologue setting up 3, and a small movie that details the very first people to use Keyblades. 2.5 is the halfway point between 2 and 3 and is KH2, KH Birth By Sleep (a prequel, think the Star Wars prequels where it basically sets up everything you've known so far and cements why things ARE the way they are in the KH world), and then another movie based off a DS spinoff game called Re:Coded (not super important if you wanted to skip this entirely). That one was a movie that included every cutscene from the DS game made into a full featured movie.
So the main thing is 1.5 was a halfway point between the first and second game, and included KH1, KH Chain of Memories, and 358/2 Days (DS game and one of my favorites). Yeah the naming scheme is a little daunting until you look all of it up.