[Update #2]: World of Warcraft: Cataclysm will be getting the Classic treatment and many new improvements in 2024.
[Update]: Wrath of the Lich King Classic will be getting new dungeons and the legendary Icecrown Citadel raid on October 10.
If you're in the mood for a bit of a challenge, or if you just want to replicate the atmosphere of the original World of Warcraft, you should definitely give the freshly launched Hardcore servers a try. The basic gist of it is that in the Hardcore realms you only have a single life to work with. Reincarnations, resurrections, soulstones or even the classic bubble + hearthstone combo will not save you!
Despite being the same game, the increased stakes make it a much, much more compelling experience, especially when it comes to social interactions as there is both safety and danger in numbers! Everything you do matters, and every risk comes with a chance to erase dozens of hours of gameplay. It's not for the feint of heart, but I'd definitely recommend giving it a try if you want to see World of Warcraft in a completely different light.
Before you dive in, there are a few things worth mentioning. First and foremost, the focus is on the PvE journey towards level 60, so PvP works a bit differently. Battlegrounds are completely disabled as they simply don't function with permadeath on, while the only way to fight enemy players is to actively flag yourself for PvP by typing /pvp and finding someone else that has done the same. If you're so inclined, you can also challenge 'friendly' players to a duel to the death, and if you win you'll even get a fancy cosmetic buff to denote your triumph!
Additionally, since the stakes are so high, the Hardcore servers have a much harsher stance towards any sort of griefing. Trying to kill other players by pulling elite enemies towards them, deliberately causing wipes in dungeons and raids or other such deceitful acts will result in major punishments, including account closure. In order to make sure this system doesn't get abused, Blizzard is also planning to dish out the same sort of punishments for people misusing the report system, so hopefully there won't be too many false reports flying around.
The final thing worth mentioning is that all of the lower level dungeons have a 24-hour lockout timer in order to ensure that people actually explore the world and mingle with their fellow players. A good thing too, because World of Warcraft: Classic is at its best when there's hordes of people running around and partying up.
If you're interested in all of the details you can check out the full list of rules and tweaks over at the official website. Enjoy, and here's to hoping you'll last longer than my first character that didn't even crack level 10 before gravity betrayed him!