The biggest problem, IMHO, is that different people want different things in adventures, but the industry & community haven't really done a good job of defining categories of audience. (Which would surely be imperfect, but would be better than the scatter-shot & hope you hit enough that we have now.) It's hard to judge good design if you don't know who the audience is.
Also, modules often have a purpose beyond being an adventure. B1 tried to teach DMing. B2 tried to teach a bit of DMing & also dungeon/setting design. The Sunless Citadel was meant to showcase the new edition. Some modules are intended to introduce a setting. Achieving such a purpose in as natural way as possible is an important aspect of good design.
Also, modules often have a purpose beyond being an adventure. B1 tried to teach DMing. B2 tried to teach a bit of DMing & also dungeon/setting design. The Sunless Citadel was meant to showcase the new edition. Some modules are intended to introduce a setting. Achieving such a purpose in as natural way as possible is an important aspect of good design.