I rather agree with Jeff here. Hey, I like stories as much as the next guy; I spend probably ten times as much time reading novels as I do playing computer games. But when I want a novel, I read a novel. When caught up in a great plot, turning a page to get to the next scene takes a lot less time than maneuvering through a dark maze or sneaking into the rebel fort.
Although scenarios should certainly have plots to help the player figure out what to do next, the plot is not the main thing. If I'm playing a computer game, I'm interested in strategy: give me puzzles to figure out how to pass, tough battles to figure out how to win, and decisions about how to improve my party so they'll win future battles as well. My favorite of the built-in BoA scenarios is not ASR, but DwtD: there's great stuff for sale, but getting the fancy armor or the excellent weapon will come at the expense of learning top-level spells, or of acquiring knowledge brews and training from the countryside. And nothing beats the fun of finding the Black Dress of Speed and then realizing that my character will have almost no armor while wearing it.
I also agree with Jeff that everyone should make the kinds of scenarios he likes; that way there will be something for everybody. For me, drop me in a detailed world with choices to make and tasks to do (real tasks, not boring courier missions with no combat that just waste time in between telling the story), and I don't really care if there's anything tying it all together or not. My characters are adventurers. They explore for exploration's sake (and the loot, of course), not because such-and-such threatens the destruction of so-and-so.