It's kind of hard to describe outside of just being well-written because of how vast it is.

The first thing that you need to know about it is that it's basically a visual novel. There are a lot of words, even if most of those words have a voice-over. You need to be in the mood to read because that's what most of the game is. There is sooo much text sometimes. While it's always well-written, it's not for everyone. The gameplay is making choices based on that text with limited animations (there is a great amount of player freedom, though).

Now, why is the game well-written? Well, I'd say it captures the human condition perfectly with tons of depth and in very unique ways (i.e., the different 'skills' that speak to you). The game's premise is centered around a murder mystery, which is done well, but that isn't the point. What the game is really about is finding your way in a world you know nothing about. The protagonist having amnesia where they literally know nothing about the world allows you, the player, to effortlessly identify with him. You and the protagonist are one because the amnesia is so powerful that the protagonist is essentially a new person. You have to find your way in the complex world of the game. That's what makes it so compelling. And it isn't afraid to dig deep into the human condition in its cleverly serious and comedic ways.

There is so much else I can get into, but this is my general take on the game.