I posted this is on of the other treads but I think it fits here.
I ran a Marine campaign a while back, it was house rules but my guys had fun and they felt really awesome at the end. This was the basic story, I’ll let you have it gratis, feel free to use it if you want. My guys DH characters had died fighting some uber-bad daemons, well most of them had died, Rick’s Cleric was like freakin immortal, no matter what I tossed at him he always lived, it made me mad after everyone else was on their third character (and no he didn’t cheat I make them roll in my line of sight). The other three guys wanted to play Marines so we made some rules and they were a Deathwatch kill team. One was Ultramarine and another was a Courier of Wrath a chapter I made up. Zach the Courier hated the Ultramarines and carried that into RP-ing calling Josh, the Ultra, Little Blue Boy. So it had the basic PC RP elements (the other one was a Raven Guard and I was an Imperial Fist). The Inquisitor was sending them (and Rick’s cleric) to gather xeno-artifacts the second (the first is special and not for free) one they went after was on an Ork world, mostly battle, no big deal, but it was too big for them to take and there were too many Orks for them to kill and call in a pick up so (as par their orders) they elected, after much debating, to destroy it. They had to sneak in and take it out. The third was on a forge world. But when they got there two of the factories where fighting over the artifact, they had to RP to find out which side to back (which involved rallying that factory) and which side to take out (strategic planning and execution of the battle) because they didn’t know which, if either, side had the thing they were after (because they investigated but didn’t do well with their rolling). Well (after much debating) they backed the wrong side and had to fight the whole other city too (so they ended up destroying both factories with proper application of gas and fire, lol, it was funny). One of them decided to ask the big question, why the Inquisitor wanted these things (if he was a heretic they’d kill him they decided) and they had to RP to get him to spill the beans, he was collecting them to build a case of heresy against another Inquisitor. So, after much debating, they kept working for him. The next artifact lead them to a tomb (a Necron tomb in point-of-fact) on a dead world. They ran across a team working for the other Inquisitor (they decided to talk to them instead of kill them outright, after much debating…a bit of a theme you may notice) who told them their Inquisitor was the traitor and they were gaining evidence against him. Well, since two guys didn’t trust our Inquisitor anyway they decided to work with the NPC’s but they woke up the Necrons in the tomb and had to fight their way out (along the way they almost died to save one of the other team, normal guys after all, which was RP-ing on their part). After a house rules space battle with a Necron fighter and fleeing from the rest of the Necron fleet (on the Rouge Trader ship they had commandeered which took much RP-ing, including treats and bribes; and much debating) they got back to the Inquisitor. They confronted him again and it was decided there would be a trial. They had to take part in it (lots of RP-ing in that) and the story built even farther past that but if you want more you’ll have to start paying me, lol.
I like the Saving Private Ryan Idea too, but I agree it'd have to be someone of more import than an Governor's son. Like an Inquisitor or Canoness... or the Governor him/herself