It's interesting to hear what went wrong with your group, so that if I do run it I can avoid those problems.
As for me, I ran it about 7 or 8 years ago, so I don't remember all the details when I ran it. Luckily, I still have an after action summary I sent to the players.
Basically, the PC's snuck in, coup de grace'd several bandits before someone woke up, and in the fight with the summoned stuff from beyond, apparently rode off with the stolen horses to escape. And no, in my campaign, that didn't lead to the End of the World. Heck, outsiders running around isn't the End of the World in D&D.
I ran it as a 1st level adventure for two guys who'd never played D&D in their lives before, and a woman who hadn't played since AD&D like 20 years earlier. So I wasn't exactly being a rat b*****d DM at this point, but I think I rolled the dice in the open (no cheating to save them and so they could get some idea of how the game worked). The rogue guy took it to right away!
<<Story: The Festival of Plenty purports to be a druidic holiday, but a guy who claimed to be an Acolyte from the Temple of St. Cuthbert says it's really a covert recruiting plan by the Sect of Sixty, a secret diabolist sect. Your investigations seem to support that claim, and that would explain why it's held out in the Deeps, away from the prying eyes of the militia. From Gorunn's conversation with a militiaman at the Culthera's Head pub, you're pretty sure Lucien really is a bandit leader, though you still don't know who hired you -- speculation turned on the Sect of Sixty because of the masks (though the meeting you were hired at was on the last day of the Festival), or merchants because they said by hitting the bandits, you were just guarding caravans in a more preventative fashion. Whoever hired you thinks Lucien didn't survive the battle, as you were paid in full for his death. You most definitely disrupted Lucien's meeting with his new ally, but you're not quite sure who the ally was -- you saw a man with a longsword and shield, who came at you at the end with a burning "wicker man" and a black dog with eyes of glowing red, both of which seemed like outsiders (not from this plane of existence). Also, that last guy yelled something about the wrath of hell -- maybe he was just being poetic? And nobody attempted to disbelieve the existence of the burning man and the black dog . . .
Experience Points:
150 xp Bandit 5 (left at 0/8 hp, tied up, and unconscious from poison)
150 xp Bandit 4 (left at -3/6 hp, stabilized at -3)
150 xp Bandit 1 (DEAD; coup de grace in his sleep -- I'd normally reduce the XP a little, but it was tough sneaking in there)
150 xp Bandit 2 (DEAD; coup de grace in his sleep)
150 xp Bandit 3 (DEAD; coup de grace in his sleep)
150 xp Bandit 6 (left at -4/7 hp, stabilized at -4, but may have burned to death)
150 xp Bandit 7 (left at -8/1 hp -- he fought very well despite his ill health; stabilized at -8, but may have burned)
150 xp Bandit 9 (DEAD; left at -3/1 hp -- bled to death, the only unlucky one)
1350 xp for Lucien
Bandit 8 ran away.
The last guy, the black dog, and the burning "wicker man" were not overcome, so no XP for them.
Total XP: 2550 xp. 850 xp each. Gorunn gets 900 xp -- 50 xp bonus for doing a good job investigating who Lucien really was and for getting the party together in the first place.
What that means: You need 1000 xp to become 2nd level. Close, but no cigar. >>
