This is not my favourite album of all time (given personal taste) but it is, in my opinion, the best studio album of all time. So, what makes the best album of all time and why is it this album?
In answering the first of these questions the following criteria might be deemed appropriate:
1. The music
2. The lyrics / concept / story
3. The production
4. The cover
5. The 'fact' that when these four criteria are put together the whole album is greater than the sum of its parts.
In answering the second question your inability to find another album that does the above better.
Be honest and admit it - you can't.