Every so often on the Bioware NWN forums, the topic of what players don't like in a module, or what makes them stop playing a module, comes up. There's one going on right now, and in the course of participating in it, it got me to thinking about what it was that's made me not finish certain modules. As such, I figured I'd go back and see if could pinpoint what it was in these modules that made me quit. I'm not going to comment on all of them, just the ones where I can specifically remember what it was that made me lose interest. In some cases, it's not that there was anything wrong with the module, but rather that it just wasn't my style. I prefer modules that feature a good amount of combat, and so modules like Almraiven and A Dance With Rogues just didn't hold my interest, even though they're excellent pieces of work.
If you're the author of one of these modules, and you happen to be reading this, my apologies. I don't mean to attack you, but I have to be honest about why your module didn't hold my interest, and I hope you take this as constructive criticism. At any rate, I think every module on this list was highly rated anyway, so it's not like my opinions are going to hurt any module's success.
Conan - Beneath the Sands of Stygia - There were two big problems with this module that stood out in my mind. The first was the visuals: the module is supposed to be set in universe of the Conan stories, and while I haven't read those stories myself, I know that they're set in a pre-medieval time. As such, the default NWN city tilesets don't fit the setting, and by using them, it ruined the immersion for me. The second, and bigger, problem was that the module was dull. After a short beginning section in a port city, the action moves to a lost, ruined city on an island. Exploring this city meant running around large, mostly empty city areas, occasionally going inside mostly empty buildings to check them out. Every so often I'd run into some wandering monsters, but those combats weren't interesting, just repetitive. Occasionally I'd have to bash down some locked doors. For some reason, these doors were made particularly tough, and bashing them down took a minute or so. I don't know why they were so tough, or even why they were locked, since there was nothing special behind them. All in all, after an hour or two of this, it became so tedious that I just gave up on the module.
One other minor, but annoying bit - in order to get to the only merchant, you had to do a lot of backtracking through empty areas, and that's never, ever fun.
B2: Keep on the Borderlands - I didn't link this one because I can't remember which version I played. I remember that this was a pretty faithful rendition of the original PnP module, and that's the problem: Keep on the Borderlands is a dungeon crawl, with no real roleplaying or story. I like action, but I need something more to stay interested.
CC1: Gates of Myth Drannor - I think this is one of those modules that rated well when there wasn't much to compare it to, but which has aged poorly since then. The beginning was ok, if unremarkable, but partway through the module, the difficulty level suddenly takes a huge jump upward. However, the merchants don't sell anything better than a cure moderate wounds potion. As such, the combat difficulty crossed the line from challenging to frustrating, and that's where I lost interest.
Desert Madness - Dark Summoning - My PC, a recently-freed slave, wanders into a nearby church, at which point the head priest decided to entrust me with a super-secret mission to rescue the princess from the castle (or something to that effect). So I go to the castle, find an ex-guard standing around, and tell him all about my super-secret mission. In turn, he tells me everything I need to know to sneak into the palace. Of course, none of this makes any sense: why would the priest give a random stranger this super secret mission? Why would I tell an ex-guard about this mission, and why would the guard help me? Bad story logic killed this one for me.
Eye of the Beholder - This one was just too hard, too frustrating, and required too much backtracking. Even with the walkthrough, just trying to figure out how to get through each level was a pain. Also, there were no merchants, and the henchmen didn't level up with me. By the time I got to the 7th level, it became obvious there was no way I was going to survive the module.
Subterra: Manastone - This module is supposed to take place in an overcrowded underground city, yet I barely saw any NPCs walking around in the streets, and the city itself had a lot of open area. Not only did that not fit the idea of an overcrowded city, but it required a lot of backtracking, and so that killed my interest.
The Last Inn - Several things killed this module for me very early on. First, I'm given a quest by a woman who tells me she has no gold to pay me, yet after I poked around various containers in her house, I found that not only did she have treasure, but also that I was able to take it without any consequence. Second, her dialogue didn't change after I completed her quest. Third, the first thing some of the NPCs said when I spoke to them was "Are you here to do my quest?" The builder put in an actual list of all the quests in the module, and the order in which I should do them. It was this last thing that put the final nail in the coffin for me. If the module doesn't even make a stab at being believable, I'm not interested.
The Paladin War - As I wrote in my comment on the module's page: "There's no attempt at realism here: you travel through a dungeon that goes from grasslands to arctic to desert with no explanation other than that the caves in the area are "weird." There doesn't seem to be much thought to why the monsters are where they are. A chest with magic items sits in the middle of an empty cave for no apparent reason."
Tomb Raiders - First, the module is supposed to take place in an Arabian Nights setting, but the starting area and the first quest location used the basic rural tileset, and none of the characters have clothing or appearances suitable to that genre. Second, the game uses a custom script that makes your gold have weight, which meant my PC was weighed down as soon as I started the module. Realism is good, but not if it's implemented for no reason and not if it makes the game less fun. Third, the only merchant in town sold only the most basic of items, so there was nothing on which to spend my accumulated gold. Fourth, the module was full of spelling and grammar errors. Fifth, there were no journal entries. And finally, the first quest location had a bug that left my character stranded in the area.