Ngaio Marsh’s detective, Inspector Alleyn, featured in a short-lived series starring Patrick Malahide & Belinda Lang. There are about 8 episodes, all set in post-war England. Most are pretty good, although some liberties have been taken with Marsh’s stories.
Hinterland, A Welsh Detective
Wallander, A Swedish Detective
Inspector Montalbano, An Italian Detective
The Young Montalbano, An Italian Detective(a prequel)
Oh yes, actually Jonathan Creek was what got me started on my mystery series kick a few years ago!
(I guess my request for suggestions for new viewing would be more useful if I could get my act together to specify what I’ve already viewed, huh? Sorry, I had totally forgotten about Jonathan Creek in this context.)
Or Bruno Cremer as Maigret. 
I endorse ‘New Tricks’ and ‘Scott and Bailey’ as well. Solid procedurals.
If you like period mysteries, how about Australia in 1920s? ‘Miss Fishers Murder Mysteries’ is very well-made and has charming characters. Two series available on DVD.
A new series of ‘Jonathan Creek’ is apparently being filmed, but that won’t help you now I suppose. Something else to look forward to.
I really tried to like that one, but it was so brutally bleak that I gave up. It makes Game of Thrones look like Cheers.
Speaking of David Tennant, we just watched the first disc of “Broadchurch” and are hooked. Only one season, but they’ll be back for a second.
The Swedish version isn’t nearly so bleak as the British version with Kenneth Branagh. Wallander even smiles once in a while in the Swedish version. 