The 6th edition brought some fundamental changes to special characters. Previously shuned characters are now amongst the greatest heroes of their kind:
Mogul Kamir - Previously the worst SC in the codex now comes with some serious buffs: Instead of being uncontrolable he now grants RR +2 attacks on the charge and delivers 3+D3 attacks himself.
Typhus - A previously medicore character who suffered from being easy to kill gained cockroach like survivability: T5 means he can't be insta-killed by anything below S10 and his FNP works against pretty much every attack. With 4 wounds it will take a while to down him.
Any more notable zeroes that became heroes?