Best debut album

Jethro Tull - This Was. Check out Steven Wilson's remixed version. I love hearing this band when they were young, just developing their style. This is primarily a blues record, a style that they ultimately abandoned. Still - listening to "Some day the sun won't shine for you", you'd swear that you could stand right up and stand amongst the band. The whole album is like that. Really enjoyable!

As an R&B lover, I'd say:

Mary J. Blige -- What's the 411
Keith Sweat -- Make it Last Forever
Lauryn Hill (solo) -- The Miseducation of Lauryn Hill
Missy Elliott -- Supa Dupa Fly (I remember seeing this in a Record Store posted everywhere, and I thought "who is she and why should I but that CD?" until I got home and listened to it.  I'm glad I took that chance.. I've loved her ever since.
 
And on another note, I really loved:
Madonna -- Madonna  (I always thought HOLIDAY would be a classic)
Nora Jones -- Come Go with Me
English Beat -- I Just Can't Stop It (my most listened to CD in college)

Michael Schenker Group S/T
Hard Rock MASTERPIECE as far as the music. Production not so much😒
What a Shame.

+1 for Chicago Transit Authority

also Kansas’s debut album is their best work, IMO

Led Zeppelin (first album), for me as a teenager, for Classic Hard Rock.
Meet The Beetles, for me as a 9-year old, the music that began it all.