Yes and no.
Story wise: There's a ton of games in the series and the storyline is ridiculously convoluted. Like more convoluted than any other game I've ever played. Just as soon as you think you've figured it out a new game comes out and makes things way more convoluted. I think the fanbase has just developed stockholm syndrome from being abused so much by the writer.
Gameplay wise: This varies across games. Some games have drastically different gameplay but the main series is overall fairly consistent and fun (also can get pretty difficult). Newer Final Fantasy games have a battle system based on the main KH series and KH III will likely be the epitome of the series as far as gameplay is concerned.
If you do play them, you should play the high definition compilation/remasters on PS4. They are called
Kingdom Hearts HD 1.5 Remixhttps://en.wikipedia.org/wiki/Kingdom_Hearts_HD_1.5_Remix
Kingdom Hearts HD 2.5 Remixhttps://en.wikipedia.org/wiki/Kingdom_Hearts_HD_2.5_Remix
Kingdom Hearts HD 2.8 Final Chapter Prologuehttps://en.wikipedia.org/wiki/Kingdom_Hearts_HD_2.8_Final_Chapter_Prologue
By the way, the characters in the Kingdom Hearts universe(s) and worlds aren't exactly the same characters as the Disney and Final Fantasy characters you are familiar with. In some ways they are but there's all this Kingdom Hearts stuff mixed in. It's kind of weird seeing these old stories altered in that way and I don't really know how I feel about it but I guess it's what I should have expected.
Also, it's mostly recently popular franchises that you'll see, so no Darkwing Duck, unfortunately.