It was fun. I actually DM'd the group in my modified 3.x adventure Red Hand of Doom, as a trial run for the Con I will be running it at. They didn't know it was coming, expecting the Bard campaign.
Players were my brother and a friend who also hadn't played AD&D in over 20 years, and one guy who never played D&D at all until 3.0 a few years ago. I had copies of the DMG and PHB for all. We hadn't expected the new guy to show, which is why I thought it would be a good night to spring the surprise AD&D night on the group.
Prep time took a bit longer with him there, but it was interesting watching his reaction. I had pregen characters, and he ended up with the magic-user and the ranger. He was trying to look up some stuff in the DMG asked "Uh, is there any sort of organization to this book?" I responded "Yeah, Gygax's stream of consciousness." We all laughed when he asked if the range of spells was really measured in inches. The dreaded THACO conversation with him turned out well, as he is an engineer by trade. :) He picked it up fast.
Prepping for the game was fast for me, after I got done writing up the pregen sheets. I basically copied them from 2 modules: the pregens in the back of Mordenkainen's Fantastic Adventure, and from Against the Giants. The copying over and looking up the gear and rules for everything else on the character sheets was essential for me as DM to rememeber the basics. There was a lot of stuff I never knew, or forgot I knew. Mostly related to combat. Gygax was clear as mud on some matters, and I realized we houseruled back in the day not knowing we were houseruling, as we never really did the surprise stuff by the book.
Nonetheless I decided to do it as by the book as I could, minus weapon against specific armor types, which I thought was an Unearthed Arcana thing, rather than a AD&D original DMG thing. I was surprised to see it there. I didn't like it in UA, and I still don't like it. So we eliminated it. We also left out weapon speed factors.
Damn I like group initiative.
The adventure went well. It was a bit faster than our 3.0 game, but not by much, I think for 2 reasons. First, we had to remember and figure out stuff as we went, like thief backstab bonuses to hit, for example. So that took longer than normal. Also, we use narrative combat in 3.0, so the time difference wasn't as great as for people who use mini's and grid combat and all the special movement and attack rules in 3.x. We don't use many of those rules in our 3.0 game.
Still, I thought we'd get more done. I think the reason why I thought we would make more progress is that the last time we played with this system was high school. We could literally play for 15 hours straight, get up the next day and do it again. Now our old working butts are tired at 11:30 pm.
Afterwards, the next day I read OSRIC's combat section, looking for more ways to streamline the combat and make it easier to explain to people. I really like how they explained, especially initiative. It's a well done book, and from what I've seen the changes they made to the system are very few, mostly minor, but good ones, like fighter specialization, fighters v. low level guys, and some magic item changes.
Playing also made me realize that AD&D is my favorite system, even more-so than 2e which I thought was my favorite for a long time. There is something grittier about it, less politically correct, and less story based. Less of a assumption that you are the "good guy". Most of what I realized I like now about AD&D 1e there was no way to appreciate back in the 80's, because I didn't read its literary influences like Vance, Howard or Leiber, nor did I have the life experiences to appreciate such a game.
I'm actually tempted to get together a regular AD&D 1e/OSRIC group now.