Wrath of the Lich King is a tremendously more ambitious - and tremendously more successful - expansion pack than Burning Crusade was, and feels like a return to the roots of Warcraft. It's more WoW, but it's a better WoW in essentially every way imaginable. No game is flawless of course, but Lich King is a title worthy of the Blizzard name and reputation. It might just remind people why exactly there are eleven million people around the world playing the game today. The Kool-Aid has never tasted so good.
Bottom Line: WoW has never been better. It's more accessible, there are more options for players than ever before, Achievements and Siege weaponry are awesome, and the Death Knight introduction is phenomenal.
Recommendation: With Wrath of the Lich King, there's been no better time to start, resume, or continue playing World of Warcraft.