So, I've been working on a set of rules for co-operative play for some time now (and have actually played a succesful mini-campaign some time ago, where a group of Imperial Guard veterans where sent to investigate a mysteriously quiet space station, but that's another story...). The core rules seem to work pretty well, so now I've moved on to the next step: creating "campaign packs" that allow for story-based campaigns based around randomly generated scenarios.
Last weekend, we got out first game in, and I'm happy to report that things went pretty well (some things still need to be ironed out, but that's the nature of homebrew; your games are also playtesting to a large degree).

Our characters, in no particular order are:
Ghanz Kurtz - A squat bounty hunter who used to belong to a cult believing that the Emperor is not only omnipresent but diffuse. He prefers not to talk about whether he still holds that belief and generally lets his axe and/or plasma pistol do the talking, but he still has all the underround contacts from his cult days, which make him an invaluable information gatherer.
"Stalker" - A bounty hunter who hails from House Delaque and who earned his nickname from the way he, slowly but surely, stalks his prey, tapping his cane softly on the flooring until they're literally caught in his webgun- web. He is adept at a strange coded sign language, which allows him to warn his comrades of danger without a word.
Calamity Joe - A Ratskin tracker, who has turned to bounty hunting as a way of life. He is an expert marksman with his lasrifle and has a Phelynx pet that he has tamed himself. He is also something of a card shark, which comes in handy from time to time.
A-C4B "Snake" - An ex-enforcer sergeant, who turned to bounty hunting after his unit was all but completely destroyed in a showdown with a (surprisingly well-organised) scavvy gang. He prefers to lead from the front, where he can inspire his comrades. Whether they believe as strongly as he does that he is their de facto leader or not is a question whose answer is shrouded in mystery, but they do seem to enjoy watching him get in over his head.

We generated an overall narrative for our campaign that we then fleshed out a bit - the emerging story is that we are on a mission to get back the deed to *redacted* for Lady Ataraxia Lockhart, so we went to a small settlement called "Fallout Post" to hunt for clues.
Then the location, scenario objectives, terrain and enemies for our first scenario were all randomly generated and as it turned out, some locals needed help flushing out some strange mutant sect known as "The Progeny of the Jubilant Kiss" who had rerouted some power generators for their own use. The locals promised to reward us not just with credits, but also with a clue - and since the tunnels even bore the name of our (slightly mysterious) employer, it seemed too good an opportunity for us to pass up. So, off we went.

Luckily, our two objectives - the generators - were not too far off from our entry point. Less luckily, the mutant leader was blocking our way and he had a lot of followers, including some strange three-armed monstrosities who seemed very eager to stop us from interfering with their power supply.
A-C4B promptly took charge of the situation (that's his version anyway), by kicking in the nearest door and opening fire with his stub gun on the three mutants guarding the first generator. Meanwhile, Stalker calmly walked up to the mutant leader and webbed him, thus neutralising perhaps the greatest danger (as we're just starting out, the enemy leaders tend to have better profiles than us, so when we saw him deploy right next to our deployment zone we were kinda worried, but the initiative deck favoured us!).
Ghanz opened another door and started walking towards the fray in his well-considered manner (some of his comrades might attribute this to his "stubby legs", but he maintains that slow and steady wins the race), while Calamity Joe ran to the enemy leader and took him out, after which he took up a firing position, as more guards milled into the big, open chamber containing the second generator.

While the team had got off to a great start, problems soon ensued; A-C4B's decision to charge into the fray proved to be more dangerous than he had anticipated, as reinforcements arrived for the three mutants he had engaged in melee and they all proved more resistant to his shock baton than expected. But Kurtz deftly picked some of them off with his plasma pistol, so things would probably turn out okay on that front.
In the big chamber, Stalker moved forwards, firing his plasma pistol at an emerging champion, while Calamity snapped off shots at a bigger group of shotgun wielding henchmen. But huge numbers of mutants, some carrying heavy weaponry was racing down the corridors towards them.