I went into Hotline Miami for the blood, style, music and combos, I stayed for the surprisingly gripping, dark as hell, weirdly affecting story.
I have yet to see the "true ending" or whatever you find out in that computer when you have the whole password, but I kept playing and might have finished most of the game in one sitting because I needed to know what was going on and where all that weird shit was going to take me.
I found especially interesting the way the game tells the story and evolves your "relationship" (or lack thereof) with that girl you save, I grew really fond of her. After all the craziness, the way you could always go back and find her was pretty cool, and the complete lack of any kind of interaction between them served as a pretty effective reflection of the dude's troubled psychological state.
Also, at the moment, my favorite song is this one: