Today at Quakecon, gameplay footage of Doom 4 was revealed. Although it is not being called Doom 4 since it is meant to be a reboot and is instead being called "Doom". To be honest I thought Doom 3 was the reboot since it followed a different setting than the first two games. Unfortunately there is no video footage to go along with this news.
The new Doom is described as being very visceral in terms of the violence and gore. This also includes reports of enemies being able to tear limbs off of the player Dead Space style. I imagine this function will only come into play when the player runs out of health but there is no confirmation of that.
With any luck there will be an official press release with the gameplay footage for everyone who wasn't able to attend Quakecon but time will tell.