I played a Radiant Servant of Pelor variant, aka a cleric who kicks butt against undead. Unfortunately there weren't any in the tomb for the six hours I played before having to leave. It shows how much I remembered! Despite the 3.5 upgrade, the adventure has a first edition feel, starting with why this crazy lich would create this tomb which seemed to serve no other purpose than to challenge adventurers to plunder it.
Occasionally there would be disconcerting things that seemed to serve no other purpose than to vex adventurers. Often you were forced to roll the dice and move through traps and portals because there was no other way forward. If I had a dime for every time the rogue searched for traps - pretty much every 5' square we traveled. After years of learning about things like "dungeon ecology" and adventure pacing, it was strange to play in this often capricious and illogical adventure. It's how we did it in the old days.
Despite the old school ways, some of my best D&D memories are Gygax adventures: Sneaking around the sleeping giants in the "G" series. The one-way stadium turn style in White Plume Mountain. The sphere of annihilation mouth in Tomb of Horrors. They're not only good memories, but iconic encounters that we all stole and used in our own adventures. These adventures stretched us, challenging us to write our own stories. I often had more notebooks in my school backpack for D&D than I did for school, as the binders of characters and adventures multiplied. I don't recall ever staring at a blank piece of paper, worried about writing a school essay, but I do remember quite a few creative blocks while staring at a blank piece of graph paper, the only deadline that matters being the D&D game with my friends that weekend.
Tomb of Horrors: Go ahead, stick your hand in there. I dare ya.
White Plume Mountain: One way in, no way out (unless you rolled your "bend bars/lift gates.")
Steading of the Hill Giant Chief: The thing with the giant adventures was the true perception that things could get out of hand very quickly. There was no adventure pacing, no safe place to rest, just a big lair of giants you're invading. This was D&D without a net and many a character never returned from these adventures. Get them angry and woken up and you're in a heap of big trouble! This sense of fear and the possibility that anything can happen is missing in todays more formulaic D&D.