With the rumors floating around about classic going into phase 6, which is supposed to drop around the end of the year, I think its time we looked at the Naxx raid which is obviously the last and hardest raid in classic wow. It also serves as the centerpiece of difficulty and has stood the test of time as one of the best raiding experiences in the whole wow.
It also introduced a whole lot of interesting loot crowned by the games first ever legendary item Atiesh, Greatstaff of the Guardian which is remade from 40 rare drop splinters that drop only from Naxxramas bosses and then theres a whole questline to remake it.
As part of the event to introduce the legendary raid, there will also be a few events called the scourge invasions which is a grim way to get players introduced to the Argent Dawn faction. For the PvE players the invasions involve killing the undead masses that are assaulting Azeroth, but there are also treats for the PvP players who get to compete for the control of the towers in Eastern Plaguelands which grant the side that controls them a significant buff to melee and spell damage which is extremely useful while raiding in the endgame.
If you're looking to brush up on your skills or just check out the Naxx mechanics you can do so on a private WOW server.