Nile: Annihilation of the Wicked, Ithyphallic, Those Whom the Gods Detest, At the Gate of Sethu.
Nile, for me, is one of those rare bands where I enjoy their later/new materiel more than the early stuff, with the possible exception of Black Seeds of Vengeance. Nile's past four albums in a row have been amazingly brilliant, and I'm looking forward to seeing them when they play in AUS in November.
Morbid Angel: Altars of Madness, Blessed Are the Sick, Covenant, Domination.
Morbid Angel's first four albums with David Vincent are all death metal classics, so much is true. But beyond the reputation, the music actually stands completely fucking firm. Often, music tends to get overrated somewhat when it has achieved "classic" status, and not these four albums. Absolutely beastly stuff with some great riffs, wildly chaotic leads and some pretty cool vocals. I consider Morbid Angel to be THE original death metal band, beating out Death.
Obituary: Cause of Death, The End Complete, World Demise, Back from the Dead.
I know, odd not to include Slowly We Rot instead of Back from the Dead, but I actually really, really enjoy the groovey kind of stuff Obituary added on The End Complete and the two albums that followed, over the raw, primitive viciousness of the debut album, though I love that too.
Runemagick: The Supreme Force of Eternity, Enter the Realm of Death, Resurrection in Blood, Requiem of the Apocalypse.
Runemagick's first four albums are just sheer death/doom goodness. Powerful as fuck guitars with a real beastly tone, and some awesome riffs and melodies throughout. Awesome stuff, with very cool cover artwork to boot.
Melechesh: Djinn, Sphynx, Emissaries, The Epigenesis.
I used to consider Melechesh the black metal version of Nile. An immature view, but one that might not be too far-stretched. Their four latest albums are just loaded with amazing riffs, and rather strong productions.
Yeah, that looks pretty good. I could add plenty of others, but many I'd pick, such as Vader, Bathory, Graveland, Deicide etc, are hampered by one slightly flawed album each in between that brings down the whole "four consecutive" album rule.