The few good things on PBS have been supplanted by cable. There are now much better science shows than Nova on the Discovery Channel. There are much better kiddy shows than Sesame Street on Nickelodeon. You can watch all the British TV you want on Hulu or Netflicks. Same for avante-garde movies and documentaries.
There really is no need for PBS any more.
My son loved the Teletubbies and Arthur and Barnie and a bunch of other shows. That was a few years ago. There is an HD version of PBS. They occasionally have some interesting history shows. They recently had a series on WWII.