The New Perry Mason had the misfortune to come along in one of the writer's strike years, 1973. Shows for all three networks were delayed, and many scripts were rushed and weak as a result. Bill Bixby's show "The Magician" was another casualty, though it managed the full season and The New Perry Mason was canned after a half season.
For fans still well familiar with the original series, this cast simply doesn't' stand up, and I write that as someone who has always liked Monte Markham. The one interesting role was Match Game regular (and Jack Klugman's eternally estranged wife) Brett Summers in the role of Gertie, the receptionist.
But Markham didn't bring the presence to the role that Raymond Burr pulled off, and none of the other actors brought the same life to their characters, either. Still, part of that may have been the writing. Scenes were too brief and rushed, and the courtroom scenes were slap-dash and brief.