TotalBiscuit got his hands on it:[link]
This game looks great, but I was unable to actually find the demo on the Steam store. Released for the US region only it seems.
Is the url required. It hasn't fully downloaded yet so I'm not sure it will even run once it's down, but it's better than nothing.
What it is:
M rated. Definitely M rated.
3rd person. Gears Of War.
Extremely faithful to WH40K as I remember it.
What it isn't:
Look out for combos when wielding the melee weapon.