This series is a spin-off to the time-travelling cop show Life on Mars. In Mars present day cop Sam Tyler, who is used to relying on offender profiling and forensics, finds himself in 1970s Manchester as the new officer on hard-man Gene Hunt's team. The past turns out to be a simpler time for cops when crimes are solved with big fists, fast cars and a copper's instinct. This led to plenty of entertaining stories that mixed drama and comedy in a seemingly effortless way that could have lasted for years, but sadly the series ended after two years and so Ashes to Ashes was born. A new character of Alex Drake goes back in time to join Hunt's team, this time in the 80s and in London. She again faces the problems Sam did of a culture clash between modern day policing methods and old style non-pc bluster.
Depending on whether or not you've seen the first series and then on whether you enjoyed its style, Ashes may provoke different reactions. It's not essential to have seen Mars to understand the format and each of the three years tries to do something different. While trying to avoid giving too much away, I'd say that each year has good and bad points.
The first year tries to be light and comedic. This was a good idea in theory as Mars had often been angst-filled and it helped to make it clear that the series is a different one. But early scenes such as Gene Hunt shooting up half of London without hitting anything from the back of a slow speedboat to the tune of No More Heroes didn't present the show in a good light. Thankfully the parody of 80s cop shows is abandoned in later episodes in favour of an involving story in which Alex decides she's gone back in time to find out why her parents died. This is an effective plot that will keep you guessing until the big reveal at the end of the year.
The second year is darker. It more closely resembles the style of Mars with an arc story involving police corruption and the show starts to explore the mystery of why cops are going back in time. The show introduces new characters, one being a mysterious stalker for Alex and the other Hunt's new boss. The resolution to the series 2 arc story isn't as effective as the first series, but I think this year's episodes are the most consistent. The by-play between Alex and Hunt is at its sharpest and funniest, and the main cop stories, which elsewhere are often routine, are engaging.
The final year provides closure and answers for both Ashes and Mars. It introduces the best new character in Keats, a creepy and charismatic antagonist for Hunt, who becomes the main focus of this year's arc story. The early episodes are the weakest as the secondary characters get more air-time than perhaps they needed along with seemingly superfluous back stories for their lives. But later it becomes clear why we've been told about their lives as the show works towards resolving the time-travelling mystery in an emotional way that allows the occasional weak moments through the three years to be forgiven. Ultimately this show is a rare one that will stand up to repeated viewings and it will be looked at years from now as being an original blend of fantasy and cop show, drama and comedy, character and plot.