The rules themselves must be flavourful and varied, using different dice rolled different ways for different things. AD&D is great because it embodies years of RPG tradition and experience, from the early days of Chainmail to the depths of Planescape, and this tradition and richness is encoded not only in the settings and stories, but in the myriad of specifics, from Bend Bars percentages to horse trait tables, artistic PCs to elf level caps. AD&D rules in and of themselves, apart from the awesome background materials, are fuel for the imagination. The gaps in them are just as important as they let that imagination run free. Learning AD&D isn't about understanding some kind of logic, it's a voyage of discovery in its own right.
Prime Junta Fun is king and a system + setting constellation can be a lot more than the sum of it's parts, but fuck some people are dense. It should pretty apparent at the most cursory glance that AD&D has a lot of flaws. They all do, in one way or another. Whether or not that is a problem is debatable, and a matter of taste.
