For about 20 sessions last year I ran Privateer Press' Witchfire Trilogy (Collected Hardcover). Now it's written for the 3e rules, but I believe in Referee (or DM / GM) innovation and free thinking during a game, making stuff up on the spot is something that goes way back the the beginning (and is something I find 'new school' with all of its formulas hampers since the players know them as well). So when I pulled this trilogy out, I did no converting on it at all. I substituted the named monsters and made stuff up on the fly to cover the rest (normal humans, hillbilly goblins, some undead witches and a bunch of other stuff).
Now I've run this three times before in different groups (though some members play across different groups so some have played it before). I wont spoiler everything, but my groups so far have had 3 outcomes: they won a moral victory but Alexia destroyed the Witchfire; Alexia tpk'd them; they won and secured the Witchfire. The first and the last were worst case scenarios...the Witchfire is a bad, BAD minor artifact-level two-handed sword. It being anywhere but the PCs hands is bad for the PCs. The first outcome I made part of Onn's history - the swamp of Whitemarsh was the location of the events in the module, the PCs were victorious but in the end Alexia destroyed the blade and the Big Hurt really happened afterwards (I won't spoil it for anyone).
Its been a few years and most of my current group are newer gamers that have never played it and so I dusted off the module again. Things were par for the course...some players liked the investigative nature of the beginning of the module, others the developing story, and so on and such. I threw in Onn-esque tidbits as well, such as renaming the Deities, making references to places in Onn and the people they encountered, as it is, the module really does drop in well with minimal fiddling to its background parts.
We got through the first module, the Longest Night, with little difficulty. Most of the monsters I needed to use were either already in existence in oldschool references or made on the fly. I used parts of the bridging module, Fool's Errand, as well. We had just got a couple sessions into the second module, Shadow of the Exile though when the party made a left turn and went off the reservation. Now, There is one thing about 99% of modules that can't be helped, they expect the PCs to follow the plot. Well I bucked the plot from day 1 myself by making changes to a bunch of things, most of which the PCs aren't aware of, but a couple of things the experienced players are.
***** WARNING, HERE BE SOME SPOILERS *****
The first noticeable HUGE divergence though happened at the climax of the Longest Night - Alexia and her animated Coven did retrieve her mother's body and the Witchfire, but only the coven made off successfully. That's right, I let the PCs kill the module antagonist fair and square. I let them keep the Witchfire, knowing full well what would happen next...and when it sunk in a session later when an older woman that resembled Alexia showed up, talking heatedly with Father Dumas...the Coven used a great magic to reclaim Lexaria, Alexia's mother, from beyond the grave.
Lexaria did manage to get the body of Alexia and the party ended up following the module loosely, travelling to the Machine Temple where they faced off against Lexaria and her still undead coven. The PCs won eventually, Lexaria was shoved off the Great Machine and fell into lightning-filled darkness, the coveners destroyed and they took Alexia's body with them, eventually cremating it.
That's when the second HUGE divergence happened...the party decided the Witchfire wasn't safe in a small town in the middle of a swamp. Father Dumas informed them a while back, the only priests powerful enough to seal the Witchfire and keep its evil at bay were at the Sactaeum, the highest temple (of his religion) located in the capitol of the Great Kingdom, far to the east.
They decided to go for it!
Now, from a module standpoint this isn't possible. From a gaming standpoint, I was about to jump out of my seat and high five everyone. Every time I ran this module, no one has said "let's go THIS way". The invasion force spearhead of Vinter was close by, they decided to AVOID it. The party has created its own mission now, get the sword safely to a place where it won't hurt anyone again and I think it rocks.
Vinter knows about the sword though, so he will be looking for it, Lexaria and the coven had more secrets buried that haven't been uncovered as of yet and there is always Vinter's right hand man, the sadistic Magic-user Vahn Oberon and that's just the enemies the PCs know.
Where we're going from here isn't defined now. The party has a long trek overland, I plan on doing it sandbox-style. I have a few planned events for them, but largely week to week I'm going to roll a bunch of dice and let the story unfold for all of us. I see alot of good oldschool exploration coming...all because of a sword, some undead and players that decided they had better chances elsewhere to do some good.
The first session of this is kicking off soon, boy I can't wait. Game On!