I consider this to be the culmination of the Storytelling system, a perfect fusion of mechanics and roleplaying.
Each Attibute category has an associated subsystem: Violence and Chase for Physical, Investigation for Mental, and Social Maneuvering for Social. Each subsystem is unique, simple mechanics that lend incredible depth to your game. Might I add, Social Chases are a stroke of genius. Not only that, but these subsystems allow players - at Storyteller discretion, of course - to contribute to the world and narrative in meaningful ways, emphasizing a collaborative angle to Storytelling.
The advancement system actively encourages rewards you for developing your character, adding to the story, and making things dramatic. Beats get everyone involved; it's incredible how someone who isn't confident or invested in roleplaying totally shifts gears once they realize that they have an entire rules structure behind them.
Chronicles of Darkness is incredibly malleable (and will be even more so once Hurt Locker drops). Need to change over to a totally different setting? Slap some flavor on there, jot down a few Conditions, invent some new Merits as you need them, and BAM. Converting older World of Darkness settings to Chronicles of Darkness has been an absolute breeze. And if something doesn't work, discuss it with the players, and give them a Beat to parley. Silky smooth.
I could go on, but I wouldn't know where to begin. The way the system focuses in on the meat of tabletop roleplaying and streamlines all the fiddly bits is something I feel no other system has done thus far. I recommend reading the book all the way through, giving it time to digest, analyzing the intent of the rules, and corroborating your findings with others. For such a small package, Chronicles of Darkness has a lot to appreciate, and every new insight you glean opens up a world of opportunities.
[5 of 5 Stars!]