I still play (A)D&D with friends from time to time, but we play the way old versions of the game. We played Basic D&D (the "Moldvay" version that came out in 1981 with the magenta box) for a couple years, since it is extremely simple and easy to run for the DM. (There was also an Expert book for when characters went above 3rd level) Recently, we jumped to the first edition of AD&D, which many of us in the group have experience with, so it isn't a tricky change for us. AD&D is definitely more involved (more rules for everything you can think of), but it doesn't have to be. The older versions of the game were almost modular... you could choose to use rules you liked and ditch the ones you didn't. (It is almost like a make-your-own-RPG kit.) You can obviously do this with newer versions, but the older versions are a bit more "rules-lite" and are easier to do this with. In fact, our DM just recently decided that he wanted to start using some of the rules (basically for combat) from the Basic/Expert game in the AD&D game to make things easier on him. Nobody complained at all. I always felt that the game is the DM's to run and he/she can do what they want.
In fact, I recommend running the game and if you don't know a rule for something, if you don't know where it is in the books and can't look it up inside of a minute, just wing-it and make something up that makes sense to keep the game flowing. Being a DM is definitely an art. I think a by-the-book rules-happy DM that is always pausing the game to leaf through books drags the game's momentum down.
All in all, I recommend the older versions to people that are daunted by the heaviness of the rules for most versions of D&D. You can get the older books from used book stores or off of eBay for quite cheap. I originally learned from the Molvay (1981) magenta boxed set, and I heavily recommend that book to newbies, since it is easy enough for a child to learn and play. :-) Once you know it well, you can always move up to more advanced rules systems, if you choose to.
btw... I recently bought a couple extra (reading) copies of the Moldvay basic rulebooks from eBay for like $3 each, so it definitely doesn't have to be a big investment, unless you want to get minty copies still in the box... with the original dice included, etc...