In my review on Scrying, I already wrote that cards that can "manipulate" the encounter deck are - generally - very strong. Ward of Protection might just be the best example of that strength. Pay 1 resource to cancel the non-weakness treachery card you just drew. It's the big "NOPE" card: Did you just drew Umôrdhoth's Wrath at a crucial moment? NOPE, you didn't. Drew a Grasping Hands with a low agility character that could possible kill you? NOPE, you didnt. This effect is just awesome, it's so strong the designers decided to build in a drawback, in that you have to take 1 horror after cancelling the treachery's revelation effect. A minor price to pay, in my opinion. With the deck building rules on the coreset investigators, the only investigators who can currently use Ward of Protection are Agnes Baker and Daisy Walker. Both have high sanity, so they can take 1 horror easily, and with Agnes, you can even turn Ward of Protection into a weapon.
With Ward of Protection being a spell, you can use your Arcane Initiate to dig for it. It doesn't cost a valuable action to use it and - as a cherry on top - Ward of Protection has a wildcard icon, so you can commit it to any skill test.
So what's not to like?
If I really have to point out a minor flaw in Ward of Protection it would be the fact that you can only use it on a treachery you draw yourself. So there is no way to help out a buddy who just drew a nasty treachery... Well actually there is.... If one of the investigators is using Scrying, you can plan the turn order in a way that the investigator who is carrying Ward of Protection gets to draw the nasty treachery so he can cancel it.
With the deck building rules for new investigators in the upcoming Dunwich Legacy expansion permitting the use of 5 lvl 0 cards form any sphere, I predict Ward of Protection becoming one of the most used cards to fill those "off-sphere" spots in your deck.