"Wrath of the Lamb" is a new DLC coming to The Binding of Isaac in late april.
Edmund McMillen the creator of The Binding of Isaac gave his fans today (6h ago) on twitter some new detail information about the new content in Wrath of the Lamb:
10+ bosses, 100+ items, 20+ enemies, 4 chapters, 1 character, 6 rooms, 40+ unlocks, 4+ new tracks, new final ending, 7+ new "random happenings" 5 new ultra rare pickups, 5 new cards, 4 new pills, 10 new challenges and buttload of new achievements!
Prize: 3$ on steam
You don't know Isaac? Play the demo for free on web without installer: http://www.newgrounds.com/portal/view/581168
source: twitter @EdmundMcMillen