These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Archive Panic: With over 3000 episodes having been made over the course of 27 years, any first time viewer who is tempted to start watching the series from the very beginning may find themselves facing a daunting task ahead of them.
Character Development: And a lot of it too. It's very easy to forget that when Inspector Dale Smith was first introduced in 1999, 'PC' Dale Smith was portrayed as being a bigot and a bully, who was brought into the show mainly to shake up the existing cast dynamic. He eventually left to join (as it was called then) SO19, the Armed Response dudes of the Met, and managed to end Bob Cryer's career by an unfortunate gunshot. When he returned as a regular character in 2003, Sergeant Dale Smith was generally shown to be a very moral and sympathetic character, and certainly by the time it was axed in 2010 he had more or less become the de facto "star" of the series.
Burnside was a relatively minor character during his original guest appearance, albeit one who acted as antagonist for the regulars. Chris Ellison's performance was so good that he was invited back to become a regular in season four, and if you ask the person in the street about their memories of The Bill, invariably they'll involve him.
Harsher in Hindsight: Kevin Lloyd's character, DC Tosh Lines, was written out (Lloyd had been sacked for drinking problems) as having accepted a job at the coroner's office. The actor died a week later.
Never Live It Down: One of his early episodes established that Jack Meadows was demoted back to DCI after failing to supervise a corrupt officer under his command. This "career glitch" (as Chief Superintendent Brownlow once called it) would occasionally pop up again in later years whenever Meadows tried to seek promotion. His inability to supervise corrupt officers also became something of a running theme, with him becoming increasingly more paranoid as people like Don Beech, Zain Nadir and Sergeant Stone ran rampant under his command...
Not as You Know Them: WPC Page was written out of the series in 2002, following her role in the 'Dave Quinnan' exit storyline. Then she was brought back a whole year later, having supposedly been "on leave" for all that time, only to immediately be plunged into a storyline where she committed murder and lost her job as a cop. And THEN she was brought back again a few months later as a "civilian" worker at the station, where what little dignity the character still had left was systematically removed, before she was finally dumped for good in early 2004. To anyone who grew up watching the optimistic and lovable WPC Page of 1992-2001, it was like we were watching the same actress playing a completely different person.
Seasonal Rot: The show's transition to Crime Time Soap was NOT taken well by old fans of the show, neither was the desicion around 2000-2001 to kill off or Put on a Bus many of the senior characters like Chief Inspector Conway.