Metal-wise I'm going to have to go with Reign in Blood- for personal reasons of course( i dont know nor can know if it is the greatest metal album ever
As for the rest of music in general- it would be just too hard- and too ridiculous to pick the best ever.
As for the Queensryche Mindcrime comment- Luminous couldnt be more wrong- Mindcrime was a landmark album, one of the first concept albums, and remarkably well done- How many metal bands can come up with such a good story, all so excellently put to music?- the guitar work of WIlton and Degarmo is good, the drums of Rockenfield are good, and Tate is sensational.