In the spirit of what Henry was saying, note that what I am about to say pertains to how I would use an adventure, not how you would run one at a con.
Requirements that published adventures often miss:
1) Good summary. Often adventures bury pertinent information deep in the background text that the DM might skip entirely, or don't make it clear in the text which details are important to the resolution of the adventure and which are sort of peripheral. A good adventure will lay bare and summarize the essential points of the adventure.
2) Good hooks. That's hooks, plural. Give the obvious hooks (money, duty, altruism), but also give out some deeper hooks that the DM can use to draw in characters.
3) Don't surmount the system, use it. This one is an artform that few master. The basic idea is to anticipate character abilities at that level and then let the characters use those abilities to their advantage at least one. One teleport proof chamber might be a nice challenge for a party; a whole teleport proof adventure is just denying characters their abilities.
4) Multiple paths to the goal/don't force a conclusion. Consider other possibilities that the players might try and plan for them. By plan, I don't mean forbid. For example, if you are being attacked by elves, and you have a diplomatic elven peacemaker, you should not forego the possibility of diplomacy.
5) Avoid plot bottlenecks. It is okay to put hard puzzle or otherwise difficult conditions in the path of an optional goal. IT IS NOT OKAY TO DO THIS WITH RESPECT TO THE BASIC RESOLUTION OF THE ADVENTURE.
6) Avoid cliches, or add twists to them. The first cliche that most people think of is "the mysterious stranger in the bar" bit. But in 3e, there is a new loathesome cliche: the "village that is under duress by the wizard/monster/bandit that was just released/took up residence in a nearby tower/cave/dungeon." This is an extremely tired plotline!
