[Update #2]: WoW: Classic's most memorable event, the Gates of Ahn'Qiraj, is set to launch this July, 2020.
[Update]: World of Warcraft: Classic is bringing back Layering in order to combat lengthy queue times and server lag, though worry not as this will only be a temporary measure.
Out of all the raids from the original World of Warcraft, the ancient Troll city of Zul'Gurub is by far my favorite one. The boss encounters are interesting without being too overbearing, the new items are some of the best you can get in the entire game, and unlike the Molten Core or Blackwing Lair, you only need 20 people to delve into Zul'Gurub. Combine that with some awesome-looking mount drops that are prestigious even a decade later, and you've got yourself a truly spectacular raid!
You can check out what Zul'Gurub looks like in-game, as well as what sort of bosses you'll be shaking down for precious loot, through the recently posted teaser trailer. Have a look, it's a rather nostalgic one:
Besides Zul'Gurub, the update has also added the corrupted Emerald Dragon boss fights, as well as an assortment of new quests in the scorched sands of Silithus. However, if you're in the mood for something completely different, then you'll also be glad to hear that the Stranglethorn Fishing Extravaganza has finally made an appearance as a part of this update. Every week a single angler will have a chance to gain some niche but supremely useful items, so prepare well and you might just be the lucky one!
To learn more about the update, as well as any feature in specific, you should head on over to the official website. Have fun!