It's tricky to write about Kentucky Route Zero because it's best to know as little as possible about it before playing. The last thing I want is to reveal too much.
That being said, I can tell you that it's not a typical adventure game in many aspects. It's closer to the new Telltale games in the fact that it has no puzzles, no collecting items, nothing to distract from the essence of the game. It's driven by dialogue, observation and exploration, any action scenes are basically non-existent. The most unique thing about it is the narrative mechanic. The player shapes the story, but not in a way that you might expect. Plus the act/scene structure is not something you see in a game every day.
The story is very reflective and melancholic, yet not self-absorbed or pretentious as it can sometimes happen. It's quite ambiguous and not at all straightforward, exploring multiple themes and leaving a lot of room for interpretation and discovery of its meaning - not a thing for everyone. It might even seem not quite coherent at times, but there's a method in this madness.
Audiovisual design is flawless. Distinctive art style helps create the vagueness and uncanny feeling of the world, perfectly corresponding with the story. There's a lot of atmosphere in almost every scene. Oh, and the scenes. Beautifully crafted, the moments they present can range from calming and touching to rather unsettling ones. And one of them is simply the most perfectly executed musical performance I've ever seen and heard in a game.
In overall it's not a game for everyone. You won't find in it a dramatic and dynamic plot, exciting action or difficult choices. What you'll get instead is a truly unique game full of beautiful, thought-provoking writing and overflowing with atmosphere.