Hello Larry was, strangely enough, the most successful TV show McLean Stevenson was ever on. After he left MASH that is. Every single show he was the headliner for was cancelled after one season. Hello Larry ran for two. He later admitted that leaving MASH was the worst career decision he ever made and... I have to agree with him.
The show itself didn't feel complete. It was shown after "Diff'rent Strokes" and was by the same producer so in order to cement this they had a couple crossovers where Larry and Mr. Drummond met as they were old war buddies. Nothing really came of it though. After those three episodes they never met again.
The story itself was of a guy on the radio giving people advice but he wasn't very good at it. He often made smart-alec responses to what the callers would call in about. After a couple episodes it was decided to change the format around and now he was supposed to focus on his two daughters. After his divorce he moved, with them, to Portland from LA for this job.
Older daughter Diane and younger daughter Ruthie. They.. were typical sitcom kids. Nothing of real note.
In the end it just wasn't interesting enough to carry along and was dropped.