While I presume that most of us make our own modules, there are times when I was big into roleplaying that I would buy scenarios if they looked interesting. So with that in mind: What do you want when you pick up a new module for a game?
I'll get things rolling:
1. Cheap or free
2. Obvious what the scenario is about from the cover art; my favorite example of this is, I think, the old adventure in Dungeon magazine for A Rose for Talakara.
3. Compelling story line
4. Boxed text brief if present
5. NPC motivation: too many "deranged/power-hungry" evil characters; let's hear some plausible motivation
6. Non (boring) linear story lines: I don't mind if all roads converge on one point as long as the journey there is interesting enough
7. Sufficient mappage: let me know roughly where things are in relation to one another