Hotline Miami is a superbly balanced, tightly tuned action game that uses retro graphics and a top-down view to give you a dispassionate distance from the actions you're carrying out on screen that grows more disturbing the more you think about it. The music and color scheme fit the game perfectly. You really, really need to play this.
Its fluidity may be something completely new...or at least very rare.
Boss fights aren't well implemented - simply puzzles that require you to die over and over again until you figure out what to do. But they're not particularly difficult, and there are only two of them, so it's a minor annoyance at best.
If I have one real complaint, it's that the game's story never delivers (and yes, I've solved the puzzle and gotten the more complete ending. and yes, I know it's leaving the door open for a sequel). Ultimately it is better at intriguing and engaging than it is at delivering on its promises.
When you start to learn the whys and wherefores, the brilliant nihilism gives way to disappointment. I think it probably would have been better if they'd left the story in the last few missions out entirely...ultimately it detracts rather than enhances...the plot should have quit while it was ahead (though the gameplay in those levels is a fun change...they're still very definitely worth playing).
I'd characterize it as a minor complaint at worst however - and I say that as a VERY story driven gamer.
Let me be clear - YOU STILL NEED THIS GAME.
Just don't play it with any children around.