Hiya.
I'm going to give a more generic answer.
What, to me, makes a horrible module/adventure, is one that is presented more as a "plot line" to a book/movie in stead of being presented as more of a "story" for a role-playing game. There is a difference between the two; the first assumes "This is the story, it goes from A to B to C, and then at D they fight the bad guy and win", while the second assumes "This is the story, it has parts A, B, C and lastly D, where the PC's fight the bad guy".
The first is a 'story' in the sense that the writer has decided that his story is more important than the players sitting around the table. It is written very much like a novel/movie/play, with set incidents and 'actors' appearing to help push the story along. All fine and dandy for a novel/movie/play...but for an RPG? Pretty much about the worse thing you could do. What if the PC's end up deciphering who that bad guy is and completely bypass B? What if they complete C and still haven't figured out who's behind everything? Or, my pet peeve, what if PC actions cause one "important to the plot" NPC to become "removed from the picture" (killed, arrested, insulted by the PCs to a point far past reconciliation, etc.)? If I read an adventure/module and find areas that are not "easily removed and or replaced", it gets a mark against it. Too many of these and the adventure/module goes in my "too much hassle to fix" bin.
The second is a 'story' in the sense that the writer has loosely defined what is going on and then roughly detailed certain key points and locations in the story that are likely to be discovered by the PC's. Each 'point' can be removed or otherwise re-worked by the DM (hopefully on-the-fly), and it won't mess with the overall story. If the PC's bypass B and go straight to C? Not a problem. If they complete C and still don't know who is responsible? Again, not a problem, add the clues they missed and hint them back to B, that the originally missed.
Oh, and one more thing. A crappy adventure/module is one that doesn't actually make the DM's job at DM'ing easier. In other words, having a full page description about how dangerous the Forest of Unyielding Terror is and that the players are daft for trying to brave it's depths *NEEDS* to have at least another page detailing random day/night encounter tables, a map of the overall area, and several maps of potential areas they might find (grotto's, hidden glens, caves, a ruined tower, etc.). Giving the DM all this information, then having the PC's pointed to the forest is only going to make more work for the DM as he's going to have to find/draw all the maps and figure out what kinds of creatures and animals can be found, etc.
So, I guess my little diatribe boils down to "linear story-telling" vs. "non-linear story-telling". The more close to the former, the worse off the adventure/module will be...IMHO, of course.
^_^
Paul L. Ming
