KH 1 and 2 are great. Then you have Chain of Memories on the Gameboy Advance, Re:Coded and 358/2 Days on the Nintendo DS, Birth By Sleep on the PlayStation Portable, 3D on the 3DS, X was a browser-based game, and throw in a few mobile games and whatnot that I'm missing.

Then the games were packaged in collections 1.5 Remix, 2.5 Remix, 1.5 + 2.5 Remix, and 2.8 Final Chapter Prologue for PS3/360/XBone/PS4. The collections include the first two big games as well as ports of the handheld ones.

Then finally after like 15 years they released KH3. Supposedly KH3 was a disappointment but I haven't played it so I can't comment on the quality.

Just hard to get excited about the series when I feel like I missed most of it.