WOW! No I hadn't heard of this... looks interesting
Darkest Of Days - The Official Site - 8monkey Labs
I like the footage, would be cool to be able to have a choice as to what weapons to use and then to replay each section with a variety of options.
And of course co-op would be awesome! I see no mention of multiplayer or co-op on the site.
I found a demo on FilePlanet..
FilePlanet: Darkest of Days Demo
...looks like it's passworded - link