Currently, Shield is almost useless as Barbarian and Monk can farm easily. They would prefer Two-handed Skorn or Dual wield instead. This situation would change when Diablo 3 Expansion Reaper of Souls comes.
Primary Skill: Punish
"10% of your shield's block amount as damage". You shield can block as well add damage as well. Crusader would be the walking killing machine. With shield in hand, they do not have to skite the enemy. With Crusader as your teammates, you can be safe to give damage behind his backs.
Secondary Skill: Shield Bash + Blessed Shield
When you see these two skill names, you can figure out that only with off-hand shield, you can use these two skills.
Defensive Skill: Shield Glare
"Light erupts from your shield, blinding all enemies 30 yards in front of you for 4 seconds". This is a cool skill. Actually it can be the primary skill. Every time you run into a monster crowd, you can use this skills to gain an upper hand.
Passive skill: Heavenly Strength
"You can wield a 2-handed weapon in your main hand while holding a Shield in your offhand. Your maximum movement speed is reduced by 10%"
It means you can pass the Skorn you have with Strength attribute for your Crusader. What's more, it can have Shield as well. This is incredible.
These five skills analysis can convince you to stock the Shield you get now. Shield investment should meet these requirements:Strength, Vitality, All resistance and +% Life. For more Diablo 3 Expansion investment, you can go to
Investment for Diablo 3 Reaper of Souls
Diablo 3 Guide: Reaper of Souls Crusader Skills Spoiler
Below is the latest Diablo 3 New Class Crusader Skills Display.