Re: Rogue Trader.
A couple of times - i've found that when played as an actual trader game the player in control of the captain makes or breaks it (deciding where to go, what deals to make, etc).
The combat/adventure side of it lays somewhere between dark heresy (fetch me a new character sheet, i've tripped and killed myself) and ascension/deathwatch (I need more damage dice...)
The trick is to not let the power level get ramped up too high or too quickly. Once the characters advance beyond a certain point the enemies needed to threaten them can turn it into a save or die kind of game, which isn't as much fun as games where players can afford to make a mess of things.
Worst fumbles i've seen ... one player managing to blow off their team-mates arm by blind firing a heavy stubber into melee (low odds to begin with, but to fumble it as well...), a player who insisted on trying to augment the (perfectly functional) drop pod guidance system, and one player who fumbled no less than four times in a row trying to drop from a valkyrie onto the top of an enemy marauder, without a parachute.
Best game... probably an investigation (dark heresy rules) into an attempted assassination where the players caught the right person, took their attempted confession (suffer not the witch to live) as genuine obedience of the creed and valid distaste of the creepy psyker character (who had moments earlier managed to desecrate the garden of the chapel trying to mindread a corpse), gave the would be assassin a pep talk, and let them go. The characters would later kick off a minor war in pursuit of an entirely unconnected individual - fortunately I had a lot of background material for the world as they missed the plot by a mile that time.
Re: Rogue Trader.
Lmao!!! Sounds kinda like what we had.
Was a premade mission, some navigator possessed by an artefact of some sorts.....
We all tried everything except restarting the warp shielding on the ship.......