Newer DAC, 3D support (meh), and 4k up-scaling, mostly. The new Mits DLPs coming out are promising 4k support.
I've intended to watch Riverworld but always missed it.
The newer, not the GT40. GT40s are like national treasures and almost never seen anymore. The Heffner GTs haven't caught a lot of attention yet, but they will in the next decade, like the Moslers and Dauer 962 LMs.