I've been watching a few British mysteries the past few weeks:
Hercule Poirot - Evil Under the Sun
Haven't quite finished it just yet, but it's really, really good. It's well-shot and well-made, with fine acting all around and exceptional acting from David Suchet as Poroit. I've found that I really like the more eccentric detectives [such as Sherlock Holmes, Poirot, and so on], rather than some of the more realistic portrayals of detecting. This is one is nice for the setting as well, an isolated island hotel, which crams all the various characters into a relatively small location and aren't allowed to leave. You really can't go wrong with this, or any of the Hercule Poirot mysteries from the past twenty years.
Murder Must Advertise
Lord Peter Wimsey mystery miniseries from book series by Dorothy L. Sayers. Wimsey is a bit like Sherlock Holmes, only much worse. He is, at time, very serious and at other times, particularly when he doesn't want to let on how much he knows, very flippant and even condescending. He's fun to watch though and this mystery, centered around dope peddling, is pretty good. It's flimed a bit small and has only a few outside shots across 4 hour-long episodes and the 30's British lingo is hard to follow at times [especially when some of the characters talk very quickly], but none of those things are enough to not recommend it to someone that likes British mystery.
A Taste for Death
Inspector Dalgliesh miniseries from the book series by P. D. James. This has been my least favorite of the three. It feels much slower paced and is packed full of characters, so it's a bit dull at times and also somewhat hard to follow. The series is also much more serious and Dalgliesh is much more normal and far less prone to eccentricities. It's all more realistic and dramatic, packed full of characters with twisted motives and lots of secrets. Not a bad miniseries, it's got its moments and story is intriguing at times, but I tend to enjoy the ones that are more fun to watch.