Well, I'd say they're not too good, because most of the tombs were plundered within years (or less) of their completion. A previously unknown (non-royal) tomb (I think the guy's name was "Oofa") was found in the last ten years or so, completely untouched and unheard of, but it was pretty nondescript. The sarcophagus was really neat, carved stone caricature (as we'd call it) of the dead guy.
The Great Pyramid of Khufu was open during Roman times (and presumably somewhat before), and tourists visited it back then. Already it was empty, meaning that it had been plundered somewhere in the pharaonic times.
Sometime near the end of the empire Khufu was resealed for some reason, leaving it to the Moslems to dig a new way in during the Middle Ages. During the Old Kingdom, after construction was complete (or perhaps just before), an earthquake shook the Great Pyramid so badly that the massive corbels over of the Grand Gallery are only hanging on by a fraction of an inch on one end. The Old Kingdom Egyptians dug up through the rock to check the corbel over the king's burial chamber, rather than disturb the king. My wild guess is that Khufu's tomb was desecrated during the 5th dynasty or during the First Intermediate Period.
Even Tut's tomb was entered in ancient times, but the burial chamber wasn't reached (see that Theban Mapping Project link, s'cool). At some point shortly thereafter, another tomb construction led to the tailings accumulating over the entrance to Tut's, and it vanished from the attention of the thieves. Typically, the Valley of the Kings tombs were plundered by those doing the work on them.
Have you read Thomas Hoving's book on the Tut discovery? Fascinating read. It was the first indication I had that Carter and Carnarvon and their party actually entered the tomb the night it was discovered, instead of waiting for the authorities as per the official story.