I must say I became quite obsessed with FLCL.
But it was the animation that drew me in because it was so beautiful. The music was AWESOME. I just loved the characters.
I'm not sure if Rahxephon would be considered a 'guilty pleasure'. It's got a few things in there to make you go 'wha..?', but I myself wouldn't really consider it that way. I like anime that make you think and have inside messages. I don't really have TOO many you'd consider guilty pleasures...
Scratch that. Onegai Twins is probably one. But then again, it's the animation and characters that drew me in. Sorry.