@Tim_Eagon I immediately thought about the difference between running Pathfinder 1e's Rise of the Runelords vs. the 13th Age intro adventure or the few AD&D 2e modules I have used.
PF has information scattered about not just in the module but across multiple books (or the SRD). It's a real pain, at times, to run the campaign. It's also designed for a party of 4. Add an extra player or take one away, and the delicate balance falls apart.
The others I listed included relavent stats as blocks when needed in the module. In some cases, they described how to vary encounters for different sizes of PC parties.
The thought that went into designing a module that is technically more sound is way easier for me to use. They thought out what people needed and provided the bare basics right there at hand rather than pointing the GM away from the module.
I also like it when flavor is included, but there are also implicit reminders for the GM to make the campaign their own instead of feeling like the material, as provided, is sacrosanct and immutable.