Hey all,
I have enjoyed playing both systems -- certainly the mechanics of 3d are written with several years of 'gaming experience' more than oAD&D, which was really breaking new ground with every supplement (some of it worked, some of it didnt -- a couple of my friends in high-school retitled 'Unearthed Arcana' to 'Dug up Junk' -- though we used some of the material found there, particularly the spells and such). Certainly some of the rules in oAD&D were wonky, but I think what many people enjoyed and still enjoy about a system like that is the gray areas that let a DM and party wing it to keep the game moving without resorting to stopping a session to flip through the rules and find the 'law'. I've enjoyed DMing both editions, but I find that in general players are less willing to go along with house rules on the fly when they have a book full of official rules to look through -- especially if they feel those rules (whether better, worse, simple, convoluted, or broken) are more to their advantage in-game.
Certainly the flexibility of character in 3e is there for all to behold -- making your sleek nimble fighter or burly theify-thug type are all there. We certainly did that in oAD&D, too, there just weren't rules for it. I find that some of the best stuff about 3e is also some of the worst, in that you come to expect some sort of rules reward for every quirk of character, rather than playing a character the way you want and finding out how that plays out along the way. Moreso in 3e than in oAD&D, I've Dm'd people playing multiclass characters simply to maximize their power in-game, rather than because they thought it would be a neat character to play. Since oAD&D was SO much about straight archetypes, character was how you played it, rather than whether or not you took 2 levels of rogue so that your front-loaded ranger could get evasion (which I find to be more the topic of discussion on these boards than how to make interesting characters).
That's not at all 3e's fault, as it's a sleeker, better designed and better executed ruleset than oAD&D in my opinion. It just makes those traps much easier to fall into (well, traps for me in my enjoyment of the game, maybe not yours). I've left a couple of 3e campaigns because I thought I'd get as much enjoyment min/maxing in Baldur's Gate on the computer -- that's certainly all that was happening on paper with to folks I was playing with.
Cheers,
Moorcrys