I went on one about a month and a half ago. They run sat and sun from 10-2 i believe. They let us through to the heisman room, up to the press box, around to the old weight room, on the field, and down the hall of all-americans.
If you are in Lincoln and have nothing else to do and you haven't seen it, then definitely go. If you are here for every home game, its not anything special. It is always fun to go onto the field, but with the construction i don't know what will be open.
I can't wait until they open the new North end up. I will definitely go again when that opens.