As players reach level 70 and begin to work on their Karazhan attunement, run Dungeon 3 instances and begin to gather the gear set that will carry them through Tier 4 and Tier 5, they will begin to consider playing the five man instances of the Burning Crusade on Heroic mode. Much like in games of yore when we beat our favorite game and then proceeded to replay it on god mode for extra bragging rights, Blizzard has introduced a game mechanic that makes dungeon re playability sensible and valuable for the average player.
Heroic mode dungeons require reputation based keys from each of the five Dungeon 3 factions. Revered with Honor Hold is required for the Hellfire Citadel key, Cenarion Expedition for the Coilfang Reservoir key, Lower City for the Auchindoun key, Shattar for the Tempest Keep key and finally Keepers of Time for the Caverns of Time key.
Once you reach Revered with a given faction, you can purchase the Heroic key from the faction Quartermaster, and the group leader may then select dungeon difficulty in the group options tab on his picture tool tip. So why run Slave Pens on hard mode, you ask? Well, the answer is gear, fun, and relevant quests.
Thus far I have seen the vast majority of epic loot available in Karazhan and from the first boss Maulgar in Gruul's Lair, and I can attest that many Heroic rare and epic grade items are superior to the raid sets available currently. Blizzard has stated that they will be looking at these sets to provide a much needed buff, but until that time, the smart player is learning Heroics and gathering the best loot possible.
Difficulty is scaled dramatically. Five decently geared level 70 players entering non-Heroic Slave Pens would have very little trouble plowing through the instance, however Heroic Slave Pens requires precise actions, focus and a well skilled and reactive team. Balance, crowd control and constant vigilance is essential as every mob can one shot a healer or DPS and healing the tank is a constant strain on mana and timing efficiency.
The concept introduced by Blizzard is truly exceptional. They have created an avenue that normal players can find raid quality gear with just their local group of friends. Raid guilds can continue to improve their players and gear during off-nights or when all available content has been cleared, and feel as though their time is put to good use. Dungeon re playability has long been an issue for MMOs and this has made huge strides towards rectifying those problems.
I look forward to the day when I can attempt a Heroic Black Morass... O.o