Brutal Doom [official site] may be the best evidence yet that our entire world is inside the mind of a child in 1995 in bed hallucinating gore, fatalities, mutilation, gore, guns, gore, and swear words, their Global Hypercolor t-shirt turning a lurid shade of turquoise around the neck and armpits to indicate a terrible fever.
Creator Sergeant Mark IV this weekend released version 20 of the Doom mod after 18 months of work. V20 brings new gore, new dual-wielding weapons, new gore, better stealth mechanics (no, really), new gore, fancier graphics, bullet penetration, more gore, and more. And more gore.
Brutal Doom may look a lot like Doom, but it's a very different game. Most of its weapons are replaced or changed, enemies behave differently with new attacks (up to picking up and throwing explosive barrels), you can kick monsters and, of course, use gruesome melee finishers. The style of combat is pretty different.
V20 was supposed to bring a big pack of maps made especially for Brutal Doom's different play, but some need a little work so that's due separately in the next few weeks. Sergeant Mark IV is also already working on a V20b to fix some performance problems.
You can download Brutal Doom V20 over here. Plain old Doom won't cut the mustard (or run the mod), so you'll need either Zandronum 2.0 or GZdoom 1.8 (you might want to try the newer dev builds of GZdoom, as official releases are way behind).