My mom was a big Unforgettable Fire fan.. I still have the same cassette tape she bought.
When I was a junior in high school, I bought Achtung Baby -- thought it was pretty good, but U2 was still just another band.. I was still just a typical casual fan and didn't know anything of U2 other than their big commercial hits...
...that is until one weekend, a small local radio station carried their worldwide broadcast of the Dublin '93 (?) concert -- I was blown away. Just amazed.
After hearing that concert, I bought Rattle and Hum and Joshua Tree.. was amazed at how good the non-singles were.. bought Boy and October out of further curiosity (I'd never heard anything off either album -- never heard of either album, period) and was amazed at how good they were from beginning to end. I bought Zooropa the day it came out and haven't looked back.