I started this box back in '98 with my high-level 2E group. We had already enjoyed the Eye Tyrant series, a lengthy Ravenloft sojourn, followed by The Rod of Seven Parts box.
We played through the hill giants, the vampires (who almost turned one PC into a vampire), right up to the Black Academy, at which point the PCs (consisting mostly of mages and specialists, and one cleric) obliterated all of the instructors and students in a huge spell duel. It's a memorable moment to this day.
They explored the original Tomb but did not continue into the City of Moil, for during a time of rest and reflection on recent finds in the Tomb, the elf wizard of the party (Kalex) attempted to read the spellbook of a Black Academy scholar and high-level necromancer. To this day I remember him carelessly opening the text, casting no spells of protection or dispelling. Into his very laboratory was gated a nalfeshnee demon, who promptly incapacitated Kalex and gated in countless hordes of demons, leading to a planar nightmare where the wizard had to fight through his entire keep, through undead, demons, and other horrors, to reclaim his tower... The Tomb of Horrors was forgotten, Kalex (along with many allies) reclaimed his crystal tower, and that campaign soon faded into 3E.
I dusted off RttToH during the githyanki Incursion campaign. Githyanki Lich-Queen Vlaakith learned of the existence of a portal leading to Acererak's Fortress of Conclusion, found beneath a school of necromancers known as the Black Academy. PCs (mentored by Kalex, now a powerful NPC) had to deal with the necromancers there and the githyanki, who had already struck a deal with the wizards. The wizards let the PCs into the Tomb without much fuss, as the headmaster of the Academy was a former PC necromancer from the 2E game, an ally of Kalex's. Behind Sarvac's back, other wizards who feared Vlaakith also let a team of githyanki bounty hunters into the Tomb to shadow the PCs so they can either find Acererak or kill themselves trying.
Long story short, all through Moil and into the Fortress the PCs were hounded by a team of eight githyanki bounty hunters, each with 16HD, each with its own classes and prcs, each with its own niche (assassin, monk, ranger, rogue, arcane archer, order of the bow, invisible blade/master thrower, and a sorcerer). Only two of the bounty hunters, the arcane archer and the order of the bow, survived following the PCs through Moil and the Fortress, though they were both killed later in the campaign.
In the end, the last two surviving bounty hunters fled, and the PCs confronted Acererak, knocking his phylactery into the Negative. The demi-lich managed to drop a Mord's disjunction on them before being destroyed.
After Vlaakith was confronted in her Palace of Whispers and destroyed, I brought back Acererak in the form of an atropal, as my chief NPC foe (an elder vampire epic sorcerer) called back the spirit of the half-fiend demi-lich, harnessing the negative energy in the atropal to create a vast army of undead.
When HE was destroyed, the atropal Acererak fled to whereabouts unknown. The campaign has since ended, giving rise to the Age of Worms.
Whether Acererak returns or not remains to be seen.