I love the old private detective shows of the 1950's and 1960's with their jazzy musical themes and their tough heroes with a heart of gold. This early version of Mike Hammer wasn't the best, (that would be Peter Gunn), but it had the best lead actor, Darren McGavin, one of those performers who is usually the best thing in anything he's in. Another reviewer said that he 'nails' Mike Hammer and he really does. Apparently he didn't like the character, (actors are often very different from the characters they play). The theory that he played it as a spoof of private eyes is interesting. The shows and McGavin's performances are serious enough that I wonder about that. But he does seem at times to laugh his way through some scenes and give a comic touch to the show. He can handle the drama just as well. The production values are cheap but he's a whole reason to watch the show by himself.
There is one other reason: the musical theme, 'Riff Blues', (I hope dfam1, who posted a review 17 years ago asking about that finally found out that that's what they call it- there are several good versions on You-Tube). I love Harlem Noctrune, the theme used for the Stacey Keach series, but Riff Blues is equally good.
I'm currently watching an episode of this show and David Janssen's 'Richard Diamond' show each night. Both are half an hour, (meaning 25 minutes), long and contemporary to each other, (Diamond was 1957-60, Hammer 1958-60). Diamond was a network show used as a replacement show, Hammer a syndicated show, so Hammer actually has more episodes, 78 to 77. Hammer is based in New York and Diamond was as well the first two seasons, (although neither show was filmed there, except for a few scenes of Hammer). You wonder if Diamond, (which starred another one of my favorite actors in Janssen) and Hammer ever crossed paths. The actors may well have crossed paths as both series were filmed at the Republic Pictures studios in LA. Both actors later played private eyes in well-regarded series, (McGavin in 'The Outsider' and Janssen in 'Harry O'). I've checked their resumes on the IMDB and they don't seem to have acted in the same TV episode or movies, although Todd and Buzz encountered each of them along 'Route 66'.