Actually I'd have given Xanterra's GCRR Four Night Railway Adventure Package a 5-Star Excellent review were it not for a concerning train ride back to Williams on Saturday. The hotels (GCRR Hotel and the Maswik Lodge) were clean and comfortable. The food at GGRR Hotel was good, but Maswik had limited food selections, which we were made aware of. The train was a fun experience! But the staff had trouble enforcing the mask mandate on the return trip. Upon our return, I reached out to Xanterra and received a call back from the general manager. They are working on more training, and aggressively helping their staff to correct this issue.
At the South Rim, check to be sure Shuttles are running so you can get around. We did and easily saw most of the Rim while there. Weather was fantastic and there were few crowds at most of the viewpoints.
If you need a way to get to Williams from Flagstaff I recommend Williams Taxi, but make a reservation a few months in advance. They're busy.