A lot of the elements you are familiar with in 3.5 are from AD&D. It's really the roots of modern D&D.
Basic D&D (B/X, BECMI, various retroclones) will get you playing an old school dungeoncrawl the fastest. But it's really stripped down and missing a lot of quintessentially D&D stuff.
The OSR people are mostly Basic D&Ders, particularly the silver age 2.0 types who write and play "retroclones". It's kind of its own subculture...in a way it's as much "D&D for people who don't like D&D" as fourth edition is. They're very system-oriented. They see D&D as an experience that the rules should be optimized to provide. They use compu sci metaphors. They network with Forgies. More nerdy than geeky, if you know what I mean.
I used to be into that but I'm falling out of it. I am realizing belatedly and somewhat to my chagrin that this aspect of the old school movement is what is drawing the interest of the 5e designers. But anyway.
If you need to learn the game in less than a week, or if "rules light", "elegance", "symmetry", "design", are your gamer shibboleths, go with Basic or a retroclone.
Otherwise pick up the AD&D books and read them. Like put them in the bathroom and read them slowly, bit by bit absorbing them for 2 months before playing. And then be prepared to elide and bend and create rules as you play.
Or get OSRIC, skim it and play a dungeon, then if you like it get the AD&D books.