So, how about that 1E? I have to admit, my only experience with 1E was playing Pool of Radiance, so it's fascinating to read all the opinions on the various books and options.
It's not the system for everyone, I'll admit: someone who cut their teeth on 3e or 4e or any of the various other new systems might find it somewhat archaic. But for those of us who started with it and have spent years and years kitbashing it to suit what we like to play, it rocks on toast.
The core books - PH, DMG, and the three monster books - are pure gold; and Deities and Demigods isn't bad either if you de-stat the gods and just use the write-ups. After that, you really have to pick and choose what elements from each subsequent book you'll put in your game.
Back in the day, though, we had a resource that's kind of hard to replicate now: every month there'd be a new issue of Dragon with new ideas for the game. Some stuck (and turned into UA), others didn't; and each new idea in the magazine would give us new ideas in turn.
What I've found is that with a tiny bit of tweaking - namely: drop experience-for-treasure, mess a bit with the level advancement tables, and give out some experience as a "dungeon bonus" after each adventure - it's really easy to design and run a 10+ year campaign in 1e while still keeping the levels rational. The game tends to somewhat fall apart once the party levels hit double digits unless the DM is willing to do a huge amount of hammering to hold it together, so it's in your interest to hold the levels below that for as long as possible.
But your players have to be willing to accept they're not going to level up every time they sneeze. My current campaign started in March 2008 and the leading characters are just into 6th level, though there's been lots of switching between parties during that time.
(see my sig. for a link to the game logs) The last one went for over 12 years and the highest PC levels were 12th; I probably could have squeezed another level or so out of it if I'd had enough good ideas for adventures etc., but I'd run out of steam and thus sank it in favour of something new.
Hidden within the admittedly disorganized mass of 1e rules are some very elegant bits of crunch that later editions could really learn from. Clerics turning undead, for example: roll d20 against a chart, if you succeed roll d12 to see how many you get. Simple, huh? Resurrection survival % chance based on Constitution - simple, but it makes death something to be feared as there's that small chance you're truly done. Teleport risk factor - the small chance you'll end up in solid rock makes the whole teleport-commuting issue rather moot. There's lots more.
Lan-"every DM's toolbox needs a hammer to get the dents out of the rules"-efan