The series moved away from crime mysteries and became a platform for Jack Klugman to pontificate about social issues. I can't pinpoint the actual seasons, it's been awhile, but he pretty much started taking on all sorts of topics.
I'd be happy with a compete series "bundle" at a discount. I loved this show, but I know the moment I pull the trigger on every season, you'll see a complete set. On Blu Ray. With bonus features.