Cards under the Radar.
A lot of people here complain most of the time about combos or big, flashy dudes that do a lot of things.
I personally think that most Decks that are currently really good perform well because they got good low-cost cards that do a lot of things and, in my opinion, need more attention than 7+ cost cards.
Since I am playing plants most of the time the perception of a "to good" card might be a little twisted but bear with me ill try to list one card per class:
Zombies:
Alien Ooze: Alien Ooze seems like an okay card at first but its actually quite insane. I have at first underestimated how popular enviroments would become but this feels like 3 cost -6/-6 at almost any given time. It´s okay for it to be strong because beasty needed some love (I think) but still seems a little to good. It´s like water Balloons on the worst steroids you can find.
Escapt through Time: Why is this a cantrip again?
Triplication: WHYYYYY do zombies get so much good carddraw. Its something between tedious and impossible to win attrition Battles by now
Synchronized Swimmer; I think this is very very underpriced considering that her Basic stats without any use of the abilty are already really good.
Wingnut: Jesus this is good.
Black-eyed-Peas: Probably the card you can smack into every giant growth deck without a thought and rarely regret it.
Poppin poppys; I liked them before. now they are crazy good.
Banana Launcher; Because sometimes things are better than they seem at first :D feels REALLY good in combustible moss and works brilliantly for spudow
while i THINK that most people are aware about how good these are they seem to get very little recognition when talking specific decks. The unsung heroes if you want to say so. Also really good cards to get if you are new to the game. Reliable and Versatile.(aside maybe from poppin poppies....thats a legendary)