Fine, since I pointed out the obvious before and wasn't really being helpful, I'll throw in my 2 cents on some "Realism Effects" that should be put in for a 'Hardcore Mode' of sorts:
-Explosions temporarily deafen people near them
-Wounds don't do all their damage at once. They do about half on an initial hit and about half over time, meaning that if you get hit several times, you WILL bleed to death without help.
-Magazines/Clips keep their bullet count. Meaning that folks who reload only when their clips have about 1 or 2 shots left will end up with 9 clips each having 1 bullet...
-On the subject of mags/clips, every gun should have '1 in the chamber'
-Grenades should have to be switched to and thrown, not tossed on the fly
-'Stamina' where as you run, your stamina empties. It refills when you stop and stays the same when you walk. When empty, you can ONLY walk until it fills 1/4 of the way or more (IE: Catching your breath). Weight of equipment affects how quickly this drains.
-Players can be 'staggered' by heavy blows. (Screen shakes uncontrollably for a second or so as the player flies back a foot or two. Screen blurs as well.)
-Speed should decrease as health decreases, starting at 50% health. Instead of just 'moving slower', this speed decrease should be in the form of a 'limp', with corresponding sound effects and screen movement. (To see this in full effect, see the way wounds work in Rainbow Six: Raven Shield. It has you limp when wounded in an incredibly realistic way!)
-It should take a few seconds of 'startup time' when welding a door before the door's welding % actually rises. Afterall, when you start welding something, it isn't instantly sealed...you should have to fully weld it shut, THEN start reinforcing it, logically. A half-welded door could easily be pushed open. A door, after half a second of welding, isn't gonna be able to withstand a Gorefast smashing at it with all it's might!
-More, realistic gore. When you blow a specimen's head off, it should leave blood spatters on the wall, ect. When a specimen explodes from a nade, gibs should fly. Currently, this hardly happens, even when by all logic, it should!
-Limbs should be able to be shot off of specimens. Not only should this do a LOT of health damage to them, but it should limit their actions. Specs missing arms shouldn't be able to attack with that arm. For animation reasons (IE: No crawling animations), specimens could be made to 'Limp' dragging a 'destroyed' leg as if it's dead. Both legs being 'destroyed' should be enough to kill a specimen, same with both arms being 'destroyed'. This would add some strategy, as shooting off a Gorefast or Skrake's weapon arm could make their threat extremely limited.
-Teammates should drop ALL weapons (Except for the knife, medgun, and welder) when they die, along with all their ammo. (Actually, this is one addition I would like to see in the MAIN GAME, not just in hardcore mode) It's ridiculous to think that in a combat situation, someone would be unable or unwilling to search a teammate's corpse for ammo and/or weaponry!
That's all for now. Some of this would require quite a bit of work and coding, but I'm sure it's all POSSIBLE...