This has been discussed/ suggested before, but the problem is that "completeness" can be different for everyone... does "complete" mean all gems have been found? And/or that the map has been fully revealed? And/or that all tasks/ quests have been done? And/or that all monsters have been killed? And/or that all secrets have been found? And/or that all puzzles in the location have been solved?
And what about the fact that some things will re-spawn after a certain number of days? So it *was* complete, but it's not any more.
Or that while you might have gone as far as is possible with a quest for the moment, there may be a further quest to do later when something else changes or you speak to another character in another location.
And if you knew that there were still some secrets to be found, then they wouldn't really be secrets, would they?
I was originally all for the idea of being able to see whether a location was "complete" or not... but given all of the above, I've reluctantly come to the conclusion that it wouldn't really work.
