I don't have any equipment that would enable me to see high definition, so unfortunately I've never seen Star Trek apparently, and never will.
But I can imagine what the effect must feel like. I was a big fan of The Man From U.N.C.L.E., starting with its first year in black & white. We got a color TV the following summer, because I was unsubtly leaving Sears catalogs around open showing them. That fall, there was a commercial for UNCLE's new season, with Robert Vaughn saying "Don't miss our debut, in color!"
It was great until the stories started trying to imitate Batman.