New Tricks is obviously part of the old line "you can't teach an old dog new tricks". But you sure can make a fresh and intelligent murder series about retired police detectives solving cold cases. The original cast for the first 5 seasons is the same and they are superb. From Sandra, the consumed "Gov na" boss, to the slightly rain-man like detective Lane who remembers literally everything from the past, but is pretty dysfunctional when it comes to daily living.
Every actor is superbly cast and the dialog is quick and often very funny. I am not British so I often need the subtitles on to catch all the very fast and subtle English humor... but love it. This show is not PC and makes no bones about the fact that the older detectives are used to doing thing sometimes the way they used to do it, and sometimes still do.. much to Sandra's dismay. BUT they get to the bottom of the crimes, maybe not always by the book.
The series actually has 13 seasons, but after season 9 I think, the actors starts to change and while it is still good, the stellar original cast is by far the best.
Watch a couple of episodes and you will be hooked.