I had to to do this one, because this question is always easy: what's your favorite game? Kingdom Hearts. 9000%, Kingdom fucking Hearts.
Apart from the original game having such breathtaking concept art, a unique cross-over concept between Disney and Squaresoft characters, a gorgeous soundtrack, and pretty much my favorite action based command system ever, I can honestly say that the most important aspect of this game for me is the story.
Yeah, the plot. Everyone talks shit about the plot, because it is admittedly WAY too complicated, but it's honestly what makes the game so special for me. I've never cried over a video game in my life, not over any Final Fantasy (and I've played all but four of them) not over any other story-driven game that's out there... but I have cried over this game, at multiple points in the story. I have to chalk that up to superb character development and (MOST importantly) the recurring friendship dynamic. Friendship is definitely the dominating plot device used throughout the entire series, and hoo-doggy did they do a good job at hitting everyone RIGHT IN THE FEELS while developing the relationships between the trio Sora, Riku, and Kairi as well as Axel, Roxas, and Xion. For fucks sake, I write fanfiction about about Axel, Roxas, and Xion. In all actuality, the writers are pretty much assholes- they build this incredibly relatable, likable group of friends only to rip them apart in the end. The diversity and development of just about every character (even the secondary ones) keeps you engaged and often coerces all sorts of rage and dying animal noises from me.
I started playing these games when I was 15, and as soon at the start screen came on, and the theme started playing with the sound of ocean waves to compliment it, I was immediately enchanted. Even though I haven't played this series in a while (though I'm eagerly waiting for KH3) I still consider it a major source of nostalgia for me. I remember thinking that I had never seen anything so magical, and that it was a fucking video game that made my chest flutter with an indescribable feeling that I could only chalk up to someone who knows how to tug at the heartstrings of an edgy, misunderstood fifteen year old who valued her friends over everything.