One of the most brilliant analysis of dungeons was written by Melan and can be found on Enworld here.
He develops a technique of analyzing how various dungeon flows by using line diagrams. He uses it to analyze several newer and older dungeons including some classics. To summarize, dungeons that are laid out where their encounter proceed in a linear fashions are generally not as well like as those which branches and in his opinion the best dungeons are where the encounters are in various loops that allows the players the full freedom to pick where they go.
I have a post on minimal dungeons here as well as an example here. The basic gist is that if you look at what Arneson did (as shown in First Fantasy Campaign) and what Gygax did you find that what we think of as a module is an artifact of publishing tournament scenarios. What Gygax and Arneson actually used were little more than sketch notes with a only a few areas written in detail. They used random tables, general notes, and improvised as the players explored through the dungeon.
If you zoom in the above image you will see that most rooms are single line descriptions. The same for Blackmoor in First Fantasy Campaign. From long experience it is tedious to make a dungeon and especially a megadungeon in tournament style. By using the minimal approach you can cover a lot of ground (or levels) within the time that most people have to prepare for games.