If Wikipedia is correct, "New Tricks" is one of the best-loved series on British TV right now (or at least it was through the 9th series, and it still has a very large audience).
The premise is simple: a small department of the Metropolitan Police is set up to deal with cold cases and unsolved crimes. It was initially set up as a way to get the first leader of the department (Sandra Pullman, played by Amanda Redman) out of the way - a disgraced rising star. She's only allowed to hire retired police officers - as civilian consultants, not actually police officers, although this limitation turns out to be something of an advantage as the retirees immediately notice they're not subject to the more stringent rules applied to acting police. So UCOS is born, and quickly proves (with their ridiculously high closure rate) that they aren't a dead-end department as was initially expected.
As the tenth season opens, Brian Lane (Alun Armstrong) gets into trouble again over the incident that forced his retirement from the regular force. This plays out across the first four episodes, leading to some closure for him, but he's also forced out of the department. He's replaced by Dan Griffin (Nicholas Lyndhurst) who we're told in passing was recommended by Lane. Griffin's a very even-tempered guy, the polar opposite of the very temperamental Lane, but shares one thing with Lane: an extraordinary memory for facts.
The end of the tenth season sees the departure of Pullman, who is hired to work with a war crimes unit, and the arrival of Sasha Miller (Tazmin Outhwaite) as the new boss. At this point Gerry Standing (Dennis Waterman) is the only original member of the team - and word is he'll be leaving during the 12 series. I look forward to Standing's departure - he was a great character, but these days he's just tired and grumpy. Largely the writing, but also the actor.
The first series was hugely entertaining, and the second series nearly as good. Sadly, the series has declined steadily through its entire run. The good news is that it's still alright because the decline has been an astonishingly gradual one. I'd recommend anyone not familiar with the series start at the beginning and watch the first couple seasons, then stop. But if you like it at all, you won't stop there - you'll just keep watching. Which is okay, although I wish the writing was as sharp as it was in the first couple seasons. I also wish they'd fail sometimes (infrequently) instead of never: they're success rate is impossibly high. I don't think they've failed since the second season, and I find that pretty unbelievable.