Kobolds and Catacombs is the new Hearthstone expansion that offers 135 cards, including nine unique legendary weapons for each class of heroes, and a few new mechanics.
The Recruit mechanic is the most interesting one, letting you summon a random minion from your deck. It will definitely help create several fresh deck archetypes and maybe even overwhelm some of the most dominating classes in the current meta.
But only time will tell how good it is, and while you're deciding what decks to build next, here is a cheat sheet of the 15 arguably most powerful cards from the Kobolds and Catacombs set. The list includes the following cards: