Everything you should expect from a blizzard expansion the only fault her is that it doesn't have anything for newbies.
The first cool about this expansion is the death knight class. The death knights start at level 55 so you will need another character at least level 55 first. The death knights start with all green gear but by the time you finish their exclusive quest chain you will be level 58 and have all blue gear. Death knights will start out with 270 first aid as well as 270ish weapon skills which are one handed axes, two handed axes, one handed swords, two handed swords, and polearms. They can also learn one handed maces, two handed maces, and daggers. Death knights can do dps and tanking.
Next is Northrend the new continent. To get to northrend you must be at least level 68. Northrendd features many new zones and the new nuetral city of Dalaran. The are host of new dugneons and raids. The now have both 10 and 25 palyer difficulty modes. You can also queuque for randoms heroics and earn bonus money and emblems of triumph or frost. The emblems are the new badges of justice for level 80 players.
WoTLK is a great expansion and if you play WoW you should get it.