What bands do you think quit way too early? Like, man these first albums they released were so great, and then they just quit and didn't give more of themselves to the world. I think we all know about bands that overstay their welcome and just churn out the same old, same old. But on the other side of the spectrum?

For me, the four that comes to mind immediately are Anorexia Nervosa, Deathember, Chastisement and Grand Alchemist.

Might not be in the same category as some of your examples since they did manage 5 full albums plus some other miscellaneous releases, but I'm sure if they could've continued working together that Isis would've made some more amazing music. Tangential to that, it's a shame that Palms was a once-and-done

Good stuff Slumber - Fallout, only 1 album but very great one. Melodic doom.

So far, it's Overthrow, Znowhite, and Ripping Corpse.

Age Of Silence. Used to be one of my favorite bands for the tounge-in-cheek nihilism on Acceleration and its unique style. I wish they would do a follow-up to that.

Who knows what a proper Timeghoul album would've sounded like.

Maybe not that early but I wasn't ready for Horn Of The Rhino to stop making music. Especially since their last album is one of my all time favourite of that genre.

I also support Radu with Timeghoul and I would add Lykathea Aflame, Barn Burner & Quo Vadis. God there's so many come to think of it... What a tough business to be in.

On the other hand some bands reunite here and there and I'm glad to see there might be hope for Kylesa releasing new material!!!

+1 for Timeghoul
You can add Ved Buens Ende, Albino Slug, Dolorian, Pan.thy.monium, Darklord and Gorement to that list
A new Direwolf, Verdunkeln or Katharsis would also be welcome

Aenygmist and I was gonna say Atoma, but I see their still active, though no album since 2012.
I know nobody will agree with me here, but since their 2nd album is one of my favourite albums, I'll say Gallhammer, too.