I still remember unwrapping it at Christmas. We'd already incorporated the classes into our game, following the Gygax articles (re)published in Imagine magazine. IIRC I, er, "somehow" managed to roll what I needed to get a Cavalier Paladin - still one of the characters I look back on most fondly. Looking back, there must have been a ton of balance issues, but I loved the new classes, new spells (especially the way cantrips were implemented) and new treasures, though I don't remember us using any of the new races. As for others, it transformed 1e for me.