I bought Zork I, II and III for my collection, as well as Beyond Zork. I already had Zork II, but that one was a bit sparse on the materials and it was the Atari ST version. These are all the IBM PC versions.
Zork I is the solid gold version. On the one hand it’s nice to have a different version than all the other grey boxes, but on the other hand I feel like I want the grey box instead. It comes with an instruction manual, but not the nice looking history book included with the grey box and it also doesn’t have a map.
Zork II is complete with all the booklets and the map that came with the InvisiClues is also included. Zork III is complete as well and comes with a floppy for ZorkQuest. Finally, Beyond Zork is also complete and comes with 5.25 inch and 3.5 inch floppies.