You may not want to hear this, but:
1) Editing. Most of the adventures you publish, while crediting an editor, don't appear to actually have been edited. They are full of typos, errors, inconsistancies, lame story elements, badly designed encounters, NPCs that lack credible motivations, groups of NPCs who cannot possibly cooperate (for example, no languages in common), maps that don't match the written description (or is it the other way around), and awful tactics. In general, it takes me dozens of hours to "edit" your published adventures, and if they weren't a store function, I wouldn't run them at all. In general, they are amateurish to the point of being personally embarrassing to run.
2) Verisimilitude. Most adventures make hardly any sense on any level. The motivations of the NPCs are often incomprehensible, their strategy and tactics are counterproductive, the quest makes little or no sense, and in general, it is unrewarding for the players to attempt to reason about the situation. Every time I have to explain something lame, or act as if it isn't lame, I feel like a whore.
3) Challenging Enemy Tactics. Monsters tactics rarely rise above the level of "suicide by adventurer." Tactics blocks give the lamest advice, and almost never make good use of creature powers or cooperation. For example, flying creatures never take advantage of their ability to fly, but instead invariable close with the characters. If 4E is supposed to emphasize tactics, why are monster tactics so stupid?
4) Terrain. Every combat, the party is largely going to use the same few At-Will and Encounter powers, and the monsters will have an even smaller number of powers available to them. Interesting terrain that can be used by both sides creatively will make for much more variety in combat. Mostly, what I see is a haphazard mish mosh of pits, bridges, water, and difficult terrain, laid out with no apparent forethought, and which the monsters appear to make little or no use of.
5) Minimize Grind. Most combats appear to written with the notion that the best way to have a more challenging combat is to increase monster defenses and hit point. I have found that most combats take 8 rounds or more, which it at least 3 rounds too long. Better tactics and terrains are a much better challenge.
6) Don't Force Lame Skill Challenges. Because, as published, Skill Challenges are a priori broken, and nothing has been done to improve them, we instead get these arbitrarily modified challenges that force the players to participate. Instead, it's time to admit that Skill Challenges are a failure, and offer an alternate mechanism that actually works. As written, unless all characters are forced to participate, the rational response to a skill challenge is always to have the character with the best chance make all the rolls, and for all characters with sub-optimal skills to avoid rolling at all. You know this: that is why almost all recently published Skill Challenges include some mechanism to force characters to roll.
The solution is trivial. The reason Skill Challenges are a priori a failed design is that failed rolls mostly count against the party, and so in order to succeed, the party should avoid failed skill checks. Thus, only the best characters should roll. Instead, Skill Challenges should be limited not by a number of failures, but by a number of rounds, with all successes counting towards the party, but with minimal penalties for any individual failed roll. So for example, if a challenge lasted three rounds, and the outcome depended on the number of successes the party as a whole attained, then it is in the party's interest to have all characters roll, since they could all contribute successes. If the party exceeds the required number of successes, then they gain some advantage, while if they fall short, they pay some cost for failure. The margin of success or failure could determine different results.
7) Accountability. There is a section for credits, but on the whole, it appears the persons credited do their jobs poorly, if at all. Why do these people have jobs? In theory, I purchase an adventure to save me the time of creating it myself, but when I find myself spending dozens of hours de-lamifying the adventure as published, why did I give up my cash? It would take me fewer hours to create an adventure from scratch, and it would be a much better experience for the players and myself. There are a lot of people without jobs, why can it possibly be that someone is collecting an hourly wage putting out such crap? If it a gardner, a maid, or a carpet layer did as poor a job as most adventure production teams, I would be giving them negative reviews on Angie's List, and I wouldn't hire them again. Why should I give you guys a pass?
I sell a lot of D&D books, but with the exception of introductory adventures, the rest just sit on the shelf. It's gotten to the point that I only bring enough copies of an published adventure to sell to the few completists, but no more, and I don't worry about re-stocking them.
Smeelbo