From another thread:
So, let me rewrite Shield:
1st level abjuration
Casting time: 1 reaction, which you take when you are hit by an attack or targeted by a spell that does damage with a Force effect.
Range: Self
Components: V,S
Duration: 1 round
An invisible barrier of force appears and protects you. Until the start of your next turn you have a +5 bonus to AC, including against the triggering attack and you take no damage from force effects from a cantrip or spell of 1st level, including the triggering attack.
At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, you take no damage from force effects from cantrips or spells of the spell slot used or lower. The spell lasts one round per level of spell slot used to a maximum of 9 rounds when cast using a 9th level spell slot.
What do you think? How would this affect your game?