I started with A Night at the Opera because "Bohemian Rhapsody" was on it, and it has that operetto section in it, so I thought that all their songs were like that. Which in retrospect was pretty stupid to think, but hey, I was in junior high.
Anyway, I was totally blown away by the variety of styles, the stellar musicianship, the production, Freddy's incredible voice, and the two words which graced the early Queen albums: No Synthesizers!
Holy shit, that means that he's doing all that on his guitar?! Even better! I love the part in "Good Company" where the break is an entire Dixieland band, all done on guitars. Every song on that album is awesome. I eventually picked up the entire discography, but A Night at the Opera will always be my favorite.