Speculation about Aphex's Syro and whether it would sound groundbreaking got me thinking about how rarely I come across releases these days that completely change my perception of what music can sound like. Like many of you, I guess, I remember first hearing Kid A and my ears and brain just not knowing what to do with it before eventually growing to love it. Other albums which completely threw me off but which are now fond favourites (and became gateways to similar music) include:
Autechre - Amber (sounded like aliens made it)
Squarepusher - Go Plastic (Too many beats)
Fennesz - Endless Summer (weird bleepy static nonsense)
Venetian Snares - Songs About my Cats (Weird time signatures, weird rhythms, weird noises)

What were you initially incomprehensible gateway albums?