I've been a huge fan of Mick Herron's fantastic Slough House series of espionage novels, so was a bit reluctant to check out the TV series based on them since that can often lead to disappointment. But after four seasons, I figured I'd give it a shot.
It's great, and it's surprisingly faithful to the books and characters (as much as possible, really).
The idea: MI-5 (the British intelligence agency) maintains an offshoot at a location called Slough House where they send agents who have either fucked up, or who are otherwise out of the good graces of the folks in charge. They basically do grudgework and the goal is essentially to get folks to quit from boredom or frustration. But every once in a while, they end up caught up in a case.
The boss, Jackson Lamb, is a former field agent who is a legend in the division, but who now just smokes, drinks, and sleeps much of the day away. He's verbally abusive to his staff (and pretty much anyone else), and all of his agents pretty much hate him. He's played by Gary Oldman, and it's an amazing performance, making an unlikable character entertaining (it helps that he's still amazing at actual spywork). He's actually toned down from the books, but if you haven't read them, you'd never know.
And the agents are all delightfully flawed, some competent folks who just got unlucky, some less-than-competent ones who have one or two skills that still come in handy, a couple of folks who are just broken (alcoholism and PTSD). The actual MI-5 agents aren't always much better -- they may be competent, but it's an organization that's portrayed as intrinsically corrupt and self-serving, a legacy of Le Carré's take on spies.
The show's often funny, but it's an action-heavy show and one where characters die a lot (they're faithful to the books here, too). Really good stuff, and each season's only six episodes long, so they go by quickly. There are two more seasons in the pipeline, too.
Oh, and @0xbitcoiner -- it's got a fantastic theme song from Mick Jagger that was up for an Emmy, if you haven't heard it yet.