I have a collection of over 2,000 records/CD's, all inventoried in Excel, so I scanned up and down the list and found it really difficult to find a band that made multiple albums but only had one good album. I can think of quite a few bands that made SEVERAL good albums, and then went to shit (REM, Psychedelic Furs, Ramones, Siouxsie & the Banshees)
I finally found two:
The Pixies "Surfer Rosa" (1988). Raw rocking songs, produced by Steve Albini. I really can't stand any of their other albums because they seem stale and overproduced in comparison, and I sold them all years ago. I'm sure fans of the band will completely disagree with me.
Diamondhead "Lightning to the Nations" (1980). Excellent medelodic thrash metal that even people who hate metal would love. Metallica has covered half the songs on this album, and the other half are great too. Then Diamondhead prompty decided to become wimpy spandex hair metal sissies, before it was even popular to do so.