Crit chance is actually very bad on Warwick.
Because Warwick has pretty horrible synergy in some ways but awesome synergy in others its important to push what works.
For your Red, I would suggest Attack Speed or Armor Penetration. I personally use Armor Penetration for the extra damage, but attack speed will allow you to go with a different item build to get to the attack speed cap.
For yellow, dodge is a fair choice, it can end up being extremely good if you can get ninja tabi (which I may be doing myself now that his ult no longer leaves him open). I run armor in the slot right now because a Warwick with defense is extremely hard to kill in most situations.
For Blue, go off max for more attack speed or armor pen. You might also want to try using Magic Resist, for the longest time I was running Armor and Magic Resist and it definitely helped the early game fights/jungle.
For quints, I have discovered the joy of Run Speed, which helps you keep ground while your waiting for Blood Scent to activate (I've noticed with the fancy new graphics that it can take like 3 seconds before it activates)