For me, Radiohead made me realize how crappy all the music I had listened to prior was. Before it, I was all pop-punk or anything like that that was popular on the charts. Pink Floyd was the only exception to this, and it was because of them that I got into Radiohead. I had heard a lot of good from OK Computer and decided to download a few of the songs, which were great, and then I got the album. It ended up being my favorite album with my favorite song.
I got The Bends ~6 months later and was kind of disappointed. It grew a lot on me but at first it just let me down. I think the straight guitar-rock threw me off.
I got Kid A, Amnesiac, and HTTT all for my birthday last year. Kid A instantly stood out as a very cohesive piece that felt like a concept album. Amnesiac seemed like a bunch of random songs, completely unique to one another, put together. A bit closer to OK Computer, but with the rampant experimenting that they had gotten into. HTTT also let me down the first few times I listened to it. It was kind of like Amnesiac, but the songs sounded weaker. However, it grew on me.
Oh, and has anyone else seen The Most Gigantic Lying Mouth of All Time? Crazy as hell.