Well, the thing is, it'd be nice to have different sorts of Reaction AIs for the survivor. Such as, a cautious or defensive one that means instead of shooting at the boomer when it shuffles around the corner, duck behind the table do it doesn't bile you.
That requires hard cover though, and nothing except line of sight will really block the Tank's throws.
For the crazed survivors, I'd actually recommend just plain friendly fire damage. On expert, a single zombie does 20 damage. I'd say a crazed survivor should do full damage. Does it mean TPKs will happen if you aren't careful? It's expert mode ain't it?
It'd make them dangerous without being impossible, especially with the cover mechanic. Though, I'd actually recommend making the crazed survivors slightly less accurate with ranged weaponry, and cover giving a penalty for them to hit, rather than taking less damage.
And of course, Crazed survivors shouldn't be able to get Craig's except on 20s with weapons that usually have Headshot.
I would say they should have No Brainer, but the damage we'd deal with Crits means it won't matter, just like with common infected.
I would advise a boost to their health though. Say, 100 split up for normal, 150 for Advanced(spawn in groups from 2-6 now), and 300 for Expert(in groups of 3-8)
As well, as a plain suggestion that I'm not too sure about, maybe give them more stuff at higher difficulties? It'd make them even more dangerous and harder to kill, but gives the upside of having more stuff. Say, one weapon or item at normal, one weapon and one item at advanced, and a weapon, a sidearm, an item, and a throwable or pocket item at Expert. Not both, but that should make them dangerous enough. One clip for normal, if they have a weapon, and a full ammo count for the other two. Expert gets Sidearms anyway.
Just things I think might be cool to have. Other things include being able to barricade doors, cover mechanics, machine guns, C4, a plot line with moral decisions to be made, mortars, armor, a hollow-point and armor piercing round mechanic(which doesn't need to go with the armor; AP does more damage to Tanks, CEDA, and Chargers, less to Boomers, Fallen and Crazed Survivors, and Smokers. Hollow-point would be the opposite, except it doesn't do more damage to Smokers, it does more damage to Spitters instead.), and so on. I like complex games. Does that mean they're the best? Nope.
I would suggest another type of SMG(Uzi?) and a machine gun, if you're gonna have three types of shotguns. I'd also suggest multiple grenade types; maybe a smoke type, bile type, incendiary, etc.
Oh! And if what I remember of the game is true, if a Witch is on fire, she does more damage.