The largest and final expansion to The Binding of Isaac. Adds items, bosses, levels, challenges, and more to the base game.
The Binding of Isaac: Wrath of the Lamb is an official DLC expansion to The Binding of Isaac, which adds new Items, Rooms, Enemies, Bosses, and more. The DLC was released on Steam on May 28, 2012.
Wrath of the Lamb saw the addition of:
35 achievements (originally 24)
Alternative floor versions, which can randomly replace one or both levels in a playthrough. These are Cellar (Basement), Catacombs (Caves), Necropolis (Depths) and Utero (Womb).
The Cathedral, the polar opposite of Sheol and is the other option of floor to go after defeating It Lives. It features angel-based monsters (Holy Leech, Angelic Baby) and contains a New Final Boss.
The Chest, a new floor reachable after you finish The Cathedral while holding the Polaroid. It starts out with four Golden Chests in the spawn room that always spawn an item. Every room before the New Final Boss are rooms with two bosses. Beating this floor with a specific character unlocks their respective item and a Final Ending Cutscene.
New types of room: Angel Room, Curse Room, Sacrifice Room, Boss Challenge, Library and Super Secret Room.
Curses: Curse of Darkness, Curse of the Labyrinth and Curse of the Lost
Devil Beggar: an alternative Beggar who takes on a more demonic appearance (horns, black skin, red eyes) than his normal counterpart. This demon beggar does not accept money, instead exchanging hearts for items.
Reference: The Binding of Isaac wikia