Assuming I can dig it out, tomorrow I shall post scans of at least one level of my majestic megadungeon "Goblinear Crag" ... written when I was 11.
And it was also just about the most fun I've ever had in my whole life.
Which tells you, really, that for all the thinking you can do about tactics and backstory and other features of a dungeon, it really all comes down to whether you come into the game ready to have a blast.
It would be nice, when I get those scans up, to link to other people who have posted their "when I was a kid" dungeon plans. If you have done this, or know of any links with scans of people's "old dungeons," please comment so I can link up!