We played for 7 hours and are just one fifth through part 2 in the Demo!

I had them starting aboard a Deatwatch Battlebarge, where they got all their info. Then they transferred over to the Valiant. And we had a whole scene with them running through the ship burning with acidic plasma fires, screaming navy personell, and the captain shouting over the vox, all to give a little more time to the Battle brothers, it was a mood starter.

Then we had the descent with the Drop Pod, where one of the DW activated a external vidlink so they could see the Kraken launching onto the Valiant as it buckled and crumbled from internal explosions.
Then they hit the atmosphere and the link got broken, seconds later thy crashed to the chapel and got launched out. First thing they see is a few hundred PDF's screaming and shooting towards a giant horde of enemies. They run towards the Captain to get a quick overview and then launch themselves into the fray. After several push's from the rebels they finally manage to break their backs and sends them away. Two of the three DW got wounded too.
After they had a talk with the Captain/Syndalla they head out towards the PDF base, and see a huge rebel group with Medusa Siege guns hitting the base walls. The Space Wolf howls and drags forth a krak grenade and the Ultramarines apotechary tackles his way through another horde doing the same. Then the Devestator opens fire with his three last full auto bursts... And in three round with one full auto hit on each horde he breaks their morale and they flee. The Siege guns barrels gets exploded by the Kraks.

Inside the PDF base they get lauded as Heroes from the stars. But a lone sergant complains about the incompotence of the Major in the base. And it dont take much, through a quick intervie with the personell and a vox through to Syndalla to find out that the Major should be a hugely competent officer. And with that infection must be cartain so the Space Wolf just snaps the majors neck like a twig, and the apotechary do a quick autopsy so all on the base knows the full and real truth about the major.

After that, they have won them selves the support of three PDF infantry squads, they head out to the Munitorium to liberate it, as they are running low on supplies. Instead of fighting the hord at the Munitorium, they do a diverting manouver. The devestator do a strength test and gets the extra strength he needs to throw a frag grenade fifty meters into a turret tower behind the hord, and at the same time one of the pdf infantry men attrackts their attention by shooting a few wild shots, with that they sneak past them.
Inside the Munotorium, they find that all of the pdf are dead, so they sneak to the ammo storage hangar and take out the rebel General with a Bolter sniped shot too the head and in the confusion two frags are rolled into the middle of each horde and as it explodes they charge, the rebels thinking the gates of hell have opened up upon them runs as fast as they can.
Stocked up on weapons they head to the surface...

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And thats as far as we got, there where many roleplaying oppertunities, and much ingame tactics talk, planning.. The fights lasted only a few rounds, the longest only 5. The Space Marines are far from invounrable, which is good for me, as it feels suitable to the best fluff about them that I like, the Horus Heresy novels. But they where still super men capable of routing three hundred men all on their own as shots pinged against their armour and hit them in the joints almost crippling them, but still the could keep going.

(But one question popped up) How often can the Apotechary use his Medicae skill on each battlebrother? We ruled for now that he could one time max each battle scene on each marine (and that is four times total when we played).