Thought of this one while playing through T2 and starting to learn that using a shield is a good thing. But it is rather lackluster in my opinion, and only helps you very briefly.
My idea was to introduce "Charge Abilities" to shields.
These don't work like Weapon Charge abilities (hold button for a while, then release). Instead, it is based on the shield condition. If you release the shield key while the shield is RED, then the ability is activated. This requires some fairly precise timing if you are fighting lots of enemies who are decently strong, and insane patience if fighting only 1 enemy who is far weaker than yourself.
Some possible abilities:
Burst -- You basically act like a Bomb of one of the status types. So inflict everyone around you with Stun/freeze/sleep/burn/shock/poison.
Rampant Charge -- You run forward for a short distance, damaging all enemies along the path
Expulsion -- You throw all enemies back away from yourself.
Healing -- Grants you the equivalent of a health pill.
Blink -- Teleports you a short distance in a random direction
Mirror -- Grants you a unique status for 3 seconds that causes all missile type attacks which hit you to be reflected back at the attacker.
I think that some of these would be far more enjoyable than the current selection of shields where you are simply deciding which status resist to be immune to when blocking.
interesting concept. what about using the attack button to trigger instead (since you cant attack while shielding)... letting go seems odd. you'd trigger it by luck more often than on purpose i would imagine.