That, and it is one of the greatest rock albums ever.
Nope. IMO it's not. It's very overrated. If I want to listen some AC/DC I would take Powerage or Highway to Hell.
But dude, please. You are one person, one opinion. What on god's green earth gives you the impression that you can speak for the 25 million plus that bought that album? At the time - fall of 1980 - that album was LEGENDARY. It was almost the perfect blend of hard rock and balls - for the guys - and melody for the girls. I can remember Christine D. walking around eighth grade with her math book emblazoned with "AC/DC" on it. The only other band at that time to cross over like that was Van Halen (for obvious reasons; say what you want about him now, but at the time Diamond David Lee Roth was a god).
I'm a huge AC/DC fan - I just spent about a week burning the various live tracks from the Family Jewels and Plug Me In DVD sets to my network drive - and while I would go to High Voltage, Dirty Deeds, or For Those About To Rock first, that album is still worthy of it's place in rock history.
I'd also argue that Brian Johnson's voice is very different than Lemmy's. Brian has an odd tone but he CAN sing (check out the bonus tracks from Sting's "the Last Ship"); Lemmy's voice is very pitchy, and more often than not, he's flat. Finally, musically, AC/DC and Motorhead are rather different.