N4 Treasure Hunt is one of only a handful of adventure modules that I have run more than once. Each time the reactions have been good to great. It was written by Aaron Allston, whose original Strike Force book for Champions I still consider one of the greatest supplements ever written for the hobby.
The basic deal is this: the PCs begin play captured, on a slave ship. Unlike the last installment of the Slavers module series, where your mighty heroes bust out and kick ass, you are zero-level chumps who only escape a cruel fate because the ship runs aground in a storm that drowns most of the slavers. So you free yourself but it's still storming, you have no equipment, slavers may lurk around any corner intent on recapturing you, you have no idea where you are and on top of that all, you suck. It's a helluva way to kick off a campaign.
As far as I know, the rules included in the module for 0-level play appeared nowhere else. The lynchpin of the system was this chart the DM kept on each PC, tracking their class-like activities. If Bobert the PC started using the bardiche they took from the half-orc, then the DM would get out his sheet for Bobert and mark a plus sign next to each class that could use polearms and a minus sign next to each class that was forbidden from using such weapons. If Bobert tried to cast the sleep spell found in the spellbook, the DM put a plus next to 'Magic-User' and a minus on every other class.
The module is scattered with opportunities to attempt different class abilities, which effectively sorts the PCs based upon what they do to survive, rather than upon any plan or desire. It's an interesting effect. As soon as any character earns the XP needed to reach 1st level the DM looks at their tally sheet. If someone has a lot of plusses next to a single class, that becomes their class going forward. Otherwise you use categories that are net minuses to weed out various classes. E.g. "You used an edged weapon in every fight, so you definitely can't be a cleric." Alignment was similarly tracked.
The other thing that I really like about this module is that the biggest treasure in it is a small seaworthy vessel. The cover art basically depicts the last scene of the adventure, assuming anyone survives. Since the slaver ship is blown off course the small island setting for the adventure could be plonked down in pretty much any sea hex on your overland map.
If you choose to track down a copy of N4 and run it, please note that there is one part of the module that I think doesn't work. There's a ghoul encounter. It attacks the party early on, before anyone could possibly reach first level. And it does so from surprise, while the party is asleep in a place they have every reason to think is safe. With its three attacks per round and paralysis ability, that ghoul could easily turn into a total party kill. Paranoid parties will post a watch and smart ones will run from the encounter (at least the members who survive the surprise segments), but there's still a strong potential for total disaster. The last time I ran N4 I'm pretty sure I downgraded the ghoul to zombie stats.
"Man, is there anything Jeff CAN'T do when it comes to gaming? This guy is like a critical 20 every roll. Jeff can bite the heads offa five game geeks, including their sorry-ass DM, and spit 'em into a large duffel bag ONE AT A TIME!...that's just the kind of messed up bastard he is! You think yer a gamer, punk? Well..do ya? Jeff will depants your weasel-ass right in front of your grandma."