For one, plug-and-play compatibility. Why should I buy something made specifically for the X campaign or city when I use my own world? Why else did they chose the word "module?"
Next, I'd like to see more of a description for the product. e.g.:
"This module is a site-based dungeon-type adventure for 4 characters of 5th level which should take characters to 7th level after completion."
Or
"This module is a city adventure with a fluid outline and revolves around role-playing. Combat is minimal. For a party of 3rd level characters which should end the adventure at 4th level. A bard or rogue is recommended, and an evil party might not fit."
Next, maps you can map. I am frustrated by good dungeons whose maps are tough to describe to players as they waddle along the tunnels. Sure, rough caverns should be here and there, but mapping shouldn't be a constant frustration for players and DMs.
Just a few thoughts,