Well, I think the shields inside the game are good for protecting your possessor, but they're bad at PvP because they slow down the player and give the enemy an opportunity to make constant attacks on your opponent until the shield breaks, so I am bringing some ideas for enhancement of Minecraft shields.
Removes the reduction of movement of the player when using the shield, but prevents the player from running.
When the player defenses form projectiles in their directions(snowballs, fireballs and arrows), the shield will reflect them in the direction from which they came but with less force.
Onslaugh 1 & 2:
When the player defends melee attacks, the player will push the enemy backwards.
Hardness 1, 2 & 3:
When the player defends himself from a body of a body, it will be more damaged than normal.
Sorry for writing mistakes or bad verb conjugation, I'm using a translator because I do not speak English.[/pre]
Reflector the shield does well enough I'd say already but still a good idea.
Onslaught sounds like a good idea but might be tough to balance, either way.
Hardness I'd put with a Thorns on Shields maybe or something like a special fire lighting I guess more so than if I were to suggest a stun. Either way a good idea to allow more for players in tough situations and not having to use Thorns on Armour or a team mate to help out in a jam (from how I'd think about it, I don't really know). Still though I'd SUPPORT! this idea.