(I have seen the entire series. This writeup is as spoiler free as it gets.)
Broadchurch is an eight-episode murder mystery series produced by British network ITV and written by Chris Chibnall. It stars David Tennant and Olivia Colman as police detectives investigating the murder of an 11-year-old boy in a small English town. It has been confirmed that a second series will be produced, but few details are known.
Format: The town, main cast of characters and plot are all introduced in the first episode. In a spoiler-free nutshell, when 11-year-old Danny Latimer isn't home when his parents and sister wake up, they assume he's on his paper route. He never shows up at school, and his body is found on the beach shortly thereafter. The police treat his death as suspicious, and the town comes under scrutiny from both the police and the media. Over the course of the series, more is revealed about each of the main characters. The town becomes the target of media attention.
Air schedule: The series aired in Britain in the spring of 2013, then in North America and other parts of Europe that summer. Canada and the United States had different broadcast schedules, with Canadian audiences seeing two episodes per week over four weeks and Americans getting one episode weekly. The varied schedule means that people watching for the first time in the summer needed to be careful about spoilers if they did any reading online. For the most part, online communities (such as the Broadchurch group on Reddit) were careful about labelling threads that would contain key plot information.
Avoiding spoilers: A person looking to avoid major plot developments would want to not read the show's Wikipedia entry beyond the first few paragraphs (and definitely not the descriptions of the characters).
Thoughts: It's challenging to discuss the show critically in much depth without really getting into the plot, and I don't want to give anything — anything — away. I can tell you that I've been an aficionada of murder mysteries (particularly the works of Agatha Christie) for most of my life, and I'm fairly particular about these things. I found this series to be well crafted, well written, well acted and well produced. The cinematography is particularly good.
If you've spent as much time as I have with Christie-esque mysteries, you've probably developed a decent sense of what types of clues might be important and which are red herrings, but you also know that your assessment might still prove to be horribly wrong.
By the middle of the series, I had formed a few theories. One of them proved to be correct. It wasn't anti-climactic, though, because of the way the final episode was structured. I won't risk ruining anything by explaining how it was structured, but it was incredibly, almost brutally, effective. I'm still feeling unsettled by it.
In summary: I enjoyed it immensely. Some people expressed confusion that some of the clues presented throughout the series had no bearing on the puzzle's solution, but that's what red herrings are for.