Greatest debut album

If Cheech and Chong counts then we can’t discount George Carlin’s “Class Clown.”

Methinks that was his debut...

Ummm, Aqualung was not Tull’s debut album.  
I forget which one was but...

As for the bad sonics on Zep 1...?

It was a long time coming before I would have anything resembling a “decent” stereo in them days.  My second eldest brother came home one afternoon and tossed it on the house “hifi” - a tube powered faux walnut Magnavox console that dilineated our living room from our dining room.  If the pressing or engineering was poor I would not have known it because the Magnavox faux walnut console stereo no doubt wasn’t up to the task of making that obvious to me. And I wouldn’t have cared anyway.  

That aside, perhaps the most obvious one bandied about here is Big Pink. Me and my Zep, Stones, Who contemporaries could recognize that achievement even then. I also have to grudgingly agree to Boston’s debut simply due to its immense impact if nothing else.  Can’t really argue that.  It was HUUUUGE.  

And thanks to the member below who mentioned Chris Whitley.  I never heard his debut in real time, discovering him only after he passed away to the tune of “Narcotic Prayer.”  I play his playlist on my server constantly.  

Fun forum - keep it up!