I ran a whole campaign in Night's Black Agents and my players and I had a lot of fun. It's extremely well designed for genre emulation combining investigation, horror, and action. You really do feel like you're in Ronin and then you learn the bad guys aren't working for the IRA but Count Dracula (or mutant zombies or the nosferatu or some kind of Lovecraftian god). One thing I especially loved is that there's not just one type of vampire but a generation system that lets you build different types of vampires. Very different types of vampires that go well beyond the goth aristocrat from some minor province of the Hapsburg empire. Among other things, this avoids the problem of the players having read the bestiary and memorizing all the stat blocks. Go ahead and read the GM section, you'll enjoy it but you'll still be surprised by the vampires in my game. I have a few reservations, all related to Gumshoe rewarding system mastery: 1) If you're not used to Gumshoe, a few of the mechanics can be a bit confusing. For example, in theory the distinction is just investigative (I get clues) vs general (I engage in combat or other action) abilities, but some of the general abilities have complicated rules about how fast you get points back and this gives the resource management aspect of the game an aspect of system mastery. For instance, the noob might choose to put points in network and thereby make their character more flexible, since you can use network to recruit lackeys who can do anything ... except network points don't refresh. The rules make sense once you understand them, but there's a learning curve to it.
2) Character generation is a classless system based on point buys and this can make character gen a bit hard. (There are archetypes, but you still have to spend your remaining points). Pelgrane's character generation website The Black Book helps with the mechanical aspects of character generation but you still have to make choices and there are better and worse ways to do it. 3) You can spend points on a roll, the outcome of which is that you lose more points of the same type. This means that instead of thinking about how scared your character is that he just saw someone rip someone's throat out and drink their blood you're thinking about probability theory of spending points vs taking a straight roll. (FWIW, the expected value is worse if you spend points on the roll so don't do it unless you're in danger of going insane). I suggest a house rule that you can't spend points on stability rolls.

These reservations notwithstanding, I still think it's a great game. I enjoyed the campaign I ran and would gladly run it again for new players or play in someone else's campaign.