Well just played the PC version of the demo, and well.... I'm not impressed.
Yes it looks good, the voice acting is a thousand times better then the movie, and the weapons feel appropriatly designed... but...
Gameplay doesn't feel that good. The combat is very hack and slashy which I was worried about, its hard to aim and the 'execute to gain back health' system is rather meh after the first few times you do it. Yes you get a nicely gory death scene, but after you've seen the same animatation for the dozenth time you wish you could just kill them.
Shooting doesn't feel destructive enough... after emptying a half dozen bolter rounds into a basic grunt orks head to drop them, you have to wonder what type of shoddy ammo you've been given and who started building orks from adamantium.
Then there the aiming. With guns it feels too loose and unfocused, in combat with melee you can swing around pointlessly too many times while it runs through an attack animation while the orks move out of the way.
So yes, from what I've played, it looks good, the atmosphere is good and they've captured what it is to be a marine well... but the combat feels too meh, the level design is pretty much a linear 'follow this path' affair, and after one mision, I didn't feel compelled to carry on to find out what was happening storywise.
Now, its not a bad game, but it doesn't feel like a good one either. In other words, I feel this is going to be one thats 'Just for the fans'. And even then as one, I'm not that sure I'll bother buying it untill its dropped in price.