I agree. The first season had a more serious, film noir quality to it. The criminals were more sinister, and people sometimes died. In later seasons, actors like Ben Welden played the criminal parts more as comic foils rather than thugs, and the stories were geared more towards kids.
He kills a couple of gangsters in the first season and they never aired it again. Apparently a gun moll and the boss find out who superman is. He brings them to a cabin on top of a mountain. They try to climb down and end up slipping to their deaths.