Recently a local station has been broadcasting “The Rifleman” repeats with Chuck Connors which are half hour dramas. I have watched a lot of TV over the 40 years, and offhand I cannot think of any US Network long-running TV shows that were mainly dramas versus comedies or variety.
I am talking about shows with basically same cast in every episode and not shows like the Twilight Zone and Alfred Hitchcock Presents.
Allowing for commercials the length of a half-hour show is around 22 minutes. That doesn’t allow a lot of time to develop a meaningful drama.
It wasn’t uncommon in the '50s and '60s. A few I can think of:
Have Gun, Will Travel
Highway Patrol
Bat Masterson
More recently, in the late 80s, Tales from the Darkside episodes ran a half hour each. Although, again, not continuing casts.
When you consider that anthology shows like these have to introduce the characters, too (you can’t assume that you know them from previous episodes), it’s even harder to do in that 22 minutes than shows with a continuing cast.
Soap operas used to be a half hour, too. They lengthened them to an hour after the 70s. Recent half hour dramas are rare, but in the 1950s, as noted, they were more common. Heck, network newscast back then were sometimes only 15 mi nutes.
Guiding Light ran for 57 years. The series was expanded from 15 minutes to a half hour in 1968, and then to a full hour on November 7, 1977.
As the World Turns ran for 55 years and was a half-hour.
General Hospital has been on for 47 years, but the series was expanded from 30 to 45 minutes on July 23, 1976.
Oh, and how could I forget Dragnet?
There were some in the 1950s, but they phased out by the mid-60s. There were things like Branded, which ran through 1965, The Rat Patrol from 1966, Felony Squad in 1967, Peyton Place, NYPD, Guns of Will Sonnet (1968) and a handful of others, but even then, they were unusual. By 1970, I can’t see any half-hour dramas in prime time.
As far as long-running shows, there was The Life and Legend of Wyatt Earp, Bat Masterson, Tales of Wells Fargo, NYPD and Naked City
Yeah, I thought of Dragnet and Adam-12. I definitely was not thinking of daytime Soap Operas when I made the OP, although admittedly they do qualify.
There’s nothing more than personal conjecture going on here, but I believe the half-hour dramas in early TV days drew on the radio dramas that preceded them. Much can be done if you’re quick and efficient in the exposition, don’t require a lot of backstory on the characters, have a lean straightforward plot and get the dialog to move crisply. In short, simple.
The sad thing is that now that the 22 minutes is expanded to 44 and the commercials pop up every couple minutes or so, you’re not getting much more show.
Even worse is to look back at those old shows and realize how simple your tastes were and how easily you could be entertained.
What about LASSIE?
GUNSMOKE from 1955-1961 was in the half hour format and then expaned to an hour lasting until 1975.
We use Hulu to find half hour fillers between ‘ready to go to bed’ and ‘‘bedtime’’.
Search the 50s and 60s. Newhart will put me to sleep. One called Highway Patrol or some such is really representative of the decade and the genre. Sort of cute and serves the purpose.
Starring “Flabbyjaws” Crawford. A must-see show when I was in junior high school.
I would say “The Wonder Years” was as much a drama as it was a comedy, at least for some of the episodes. Ditto “Doogie Howser, M.D.” (though it was more comedy than drama) and MAS*H, which was about half and half.
Showtime has the half hour long Nurse Jackie and United States of Tara which are often much more Drama than Comedy. There was a little kerfuffle when Edie Falco got nominated and won an Emmy for a lead actress in a comedy for Nurse Jackie. I think there might have been some rules that comedy was the only category she was allowed to be nominated in because of the half hour nature of the show, but maybe I’m misremembering (maybe she was nominated there because she wouldn’t have had a chance to win the drama category).
Oh, and Toni Collette won for Tara the prior year from Falco… 
Peter Gunn
Naked City (already mentioned) had half-hour shows for its first two years.
I agree that the half-hour limit makes for shallower shows. I didn’t watch Peter Gunn or Have Gun, Will Travel when they were first broadcast. I was disappointed when I saw the reruns recently.
“Sea Hunt” although is 50 years old.
“The Adventures of Superman” with George Reeves and Phyllis Coates in the first year was a drama, albeit with a guy with powers far beyond those of ordinary men. Later as it went to color, got Noel Neill and realized it was drawing kids, it became a kiddie show.
“Adam 12”
Anybody remember John Ritter as Hooperman in 1987? It was 30 minutes long, part cop drama, part single-camera sitcom, and quite possibly the origin of the word “dramedy.”