We all know how Doom has some nice violence to it but there is a mod that ups it even more, it's called http://www.doomworld.com/vb/wads-mods/54480-brutal-doom/, which is available for the ZDoom based source ports.

Here are some videos showing it off:

http://www.youtube.com/watch?v=LTh4qcfC3QU
http://www.youtube.com/watch?v=EAsADHVUguA
http://www.youtube.com/watch?v=XCEeKlgBats
http://www.youtube.com/watch?v=MjVeNVGJX70
http://www.youtube.com/watch?v=Ga3c9ilAako
http://www.youtube.com/watch?v=zBVEUkr9GEg
http://www.youtube.com/watch?v=2YQO51hNDCE
http://www.youtube.com/watch?v=ERkTpn9k-tw
http://www.youtube.com/watch?v=I96MwCIIjmk

I dropped custom monsters in my generated maps just to play and use the originals for this.

I like the shotgun sound and the pistol being replaced by what looks like an assault rifle.