WoW - Patch 2.4 preview @ Eurogamer
The first of the new instances is Magister's Terrace, a dungeon for a party of five players, offering both normal and heroic modes and a second pop at Blood Elf lord Kael'thas Sunstrider (also the boss of the raid zone in The Burning Crusade's Tempest Keep).
It's joined by Sunwell Plateau, a new challenge for a full-sized raid of 25 players. This is intended to be the hardest raid in the game until the next expansion, Wrath of the Lich King, appears. Its final boss, Kil'jaeden - who will have to be unlocked by the combined efforts of all players on the server - is acting leader of the Burning Legion and creator of the Lich King. So, Fury of the Sunwell appears to offer a climax to the Burning Crusade storyline, and a bridge to the new adventures in Northrend, expected later this year.