Metallica's Black Album.
I was a 17-year old metalhead when that album came out and boy, me and my even more metalhead friends at the time were excited. How could the new Metallica album be bad, after their first four albums? We huddled excitedly around the school stereo system before Home Group class (the generic "I'm here, miss" class you go to before you get farmed out to the other classes during the day) as one of us held a cassette of The Black Album in his excited hand, we thought "when the bell rings for class - fuck that shit, Metallica comes first". We listened to the first song... hmmm good opening riff, nice and heavy... one minute later, the same riff is still playing. That's a bit weird. None of the band's usual twists and turns, and yes, while it was still heavy there's a definite pop feel happening as well. We start looking at each other in dismay as the song moves in the predictable pop music verse-chorus-verse-chorus-solo-chorus-fade fashion that we all liked to listen to Metallica to get away from. "Well, it IS the single, let's give them a chance, maybe the next song will be good", we said to each other. The next song comes on. Another bone-crushingly heavy riff... married to a pop song structure. We start sighing. Third song came on, same story. And on and on it went. I swear I saw tears in the eyes of my metal comrades. When the bell rung, nobody was late.