Summary (Read 1up.com article for more information)
Level Cap: 80
Skill Cap: 450
Number of Zones: 10 (tentatively), for levels 68 and above
Class: Death Knight (first-ever Hero Class)
Features: Outdoor PVP zone with siege weapons and destructible buildings.
Rather than using rage, energy, or mana, Death Knights have a special "rune sword" displayed beneath their health bar, onto which the player can etch six different runes (choose between Frost, Blood, and Unholy).
Instant Cast. 5 min cooldown.
Target is embraced by a silhouette of darkness for 6 seconds, corrupting any healing spells and effects cast upon or currently affecting the target to cause damage for 50% of their healing potential instead of restoring health. Any damage shields cast upon or currently affecting the target will also be instantly consumed, dealing 50% of their absorption potential in damage. Once afflicted with Unholy Embrace, the target cannot be afflicted with Unholy Embrace again for 1 minute.
Wrath of the Lich King will introduce a new profession called Inscription that will let players customize individual spells and abilities in their spell book -- to change the cooldown timer on a Fireball, for example, or alter the crit rate of a healing spell.
One of Northrend's 10 new zones (final count still tentative) is an outdoor PVP zone that introduces the concept of siege weapons (Meat Wagons, Steam Tanks, etc.) and destructible buildings. Blizzard describes the outdoor zone as basically a "non-instanced Battleground" where completing objectives earns world-wide bonuses for your side (Think Spirit Shard buff in Auchindoun instances). The PVP zone is entirely avoidable (if you're the carebear type), and seige weapons won't be useable outside their designated PVP area.
Having learned a valuable lesson about funneling 8.5 million players into once single starting zone with The Burning Crusade, Wrath of the Lich King lets players pick a zone on either side of the continent to start from: Borean Tundra in the west or Howling Fjord in the east. Each zone has level-equivalent quests (appropriate for approximately level 68 through 72) and one Hellfire Peninsula-style instance hub with multiple dungeon wings for level 70 characters, level 80 characters, and raiders. While Northrend immediately calls to mind ice and snow, Blizzard doesn't want to make those themes dominate Northrend completely-expect as much variety as ever, only not quite as weird and wild as Outland.
Northrend's indigenous inhabitants include a Viking-like race called the Vrykul: 15-foot-tall humanoids with a strong Norse influence. Most Vrykul you encounter will be your enemies, as they've been in Northrend so long that the Lich King holds a lot of sway over them. Another friendly race -- the walrus-like Tuskarr -- will serve as a cute little counterpoint to the lumbering undead-loving oafs.
Meh, would have like more than 1 new class. While the 58-70 stuff was GREAT in BC, the instances/pvp/grinding/ect was not that great IMO. Don't play now, but I might just pick up the exp and ding 80 and quit again.