So, Swallow the Sun has their Horror suite, that's up to 4 parts now, which I love.
Dream theater has their AA/12 step suite, which is also good: http://en.wikipedia.org/wiki/Twelve-step_Suite
Rush did it first (I think?) with the Fear series and Cygnus X-1: http://en.wikipedia.org/wiki/Fear_series
Mr. Bungle has the Sleep series (Slowly Growing Deaf, Carry Stress in the Jaw, Phlegmatics).

I like sequential story telling like that, and I like artists that have themes that grow with them.

I'm looking for more examples - nb4 Unforgiven - there are a lot of songs like this where an artist tries to rehash their former glory - I'm not sure how to say it doesn't fit the pattern, other than that it just feels wrong (Queensryche had a decade and a bunch of albums in between mindcrime 1 & 2, same with Tourniquet's Skeezix Dilemna 1 & 2). Including multiple albums on the same theme is kind of tedious, and misses the point, e.g. Saviour Machine's Legend I, II, III... etc.: there's not much point in including the specific suites, when the whole albums are meant to be parts of a whole.

So are there other sequential epics out there that I should check out? Or artists with motifs that keep coming back across their career?

Mark Jansen's "The Embrace That Smothers" saga comes to mind. It's spawn over two different bands and three albums, namely After Forever's Prison Of Desire and Epica's first and third album. It's a recurrent theme about religion and the way it causes more harm than good to the world, religious extremes, and global domination through fear of god and stuff like that. And it's pretty good actually.

Eternal Tears of Sorrow released "Angelheart, Ravenheart (Act 1: Before the Bleeding Sun)" and "Angelheart, Ravenheart (Act 2: Children of the Dark Waters)" on two consecutive albums.

I'll give a special mention to Hangar 18 & Return to Hanger by Megadeth, as well

Dragonland did this, The Book of Shadows Part I, II and III were on Starfall while part IV was on Astronomy.

Unmoored had Final State in three parts across three albums.

Then there is the series of songs by Bolt Thrower.

Start with World Eater on Realm of Chaos, then listen to Cenotaph on Warmaster, then Embers on The IVth Crusade, Powder Burns on Mercenary then finally The Killchain on Those Once Loyal.

Don't they just share the same riff? Or is there a recurrent thematic and/or story being told on them?

yes, perfect! thanks! looks like there's another Epica one as well, http://en.wikipedia.org/wiki/A_New_Age_Dawns

Ah, true. There's and explanation for that, I've stopped listening to new Epica albums exactly on that 2009 effort. But that's another story for another place. I can say though that the parts on Consign To Oblivion are very interesting and so is the concept.

Awesome. Return to the Hangar is a bit like Mindcrime II, though - despite Mustaine having sufficiently revived megadeth's career, it still rings a little hollow.

Interesting, makes you wonder if there will be a part IV to The Old House On The Hill from Astronomy.

Well, Exogenesis Symphony by Muse its a perfect example of this, check it out, you may dig it althought its not metal

http://www.youtube.com/watch?v=YEH98_Ha2aA

Themes From William Blake's The Marriage Of Heaven & Hell by Ulver is worth a listen
here´s the full album

http://www.youtube.com/watch?v=PlrW9SUCINo


Also Overkill by Overkill its an obvious example

I'm actually not looking for suites on a single album - those are all over the place, and also fun, but not quite as interesting as things that are interleaved across a longer time period.

The prog rock/metal band Riverside had their "Dream" suite that was featured across a few of their albums.

Reality Dream I & II (off the album Out Of Myself)
Reality Dream III (off the album Second Life Syndrome)
Lucid Dream IV (off the album Rapid Eye Movement II)

Kat - Diabelski Dom. Part 1 and 3 were on '666' album, Part 2 (my favourite) on 'Oddech Wymarłych Światów). Devil sounding speed/thrash.

Sacramentum did that with the two parts of Black Destiny.
Black Destiny (off The Coming of Chaos)
Death Obsession (Black Destiny Part II) (off Thy Black Destiny)

storywise Bal Sagoth have epic stories going on which are strewn across various albums of them:

The Splendour of a Thousand Swords Gleaming Beneath the Blazon of the Hyperborean Empire
Featured on the albums Starfire Burning... (Pt. I), Battle Magic (Pt. II), and Atlantis Ascendant (Pt. III).

The Obsidian Crown Saga
Featured on the albums Starfire Burning... and The Chthonic Chronicles.

The Guardians of the Astral Gate
Featured on the albums Atlantis Ascendant, and The Chthonic Chronicles.

Does it count that Metallica has "The Unforgiven" on the Black Album and "The Unforgiven 2" on Reload? Or am I just misunderstanding the thread?

I mentioned that in the post - there's also part III on Death Magnetic.
It kinda counts, but it's kinda also just trying to reclaim former glory - which there's plenty of examples of, and I don't find quite as interesting, but it's hard to explain the difference.

Awesome - can you point out which songs belong to which epic? I can't figure it out from the titles...

since grauer_mausling hasn't responded yet... I am too lazy to make a real list but have a look at this glossary from Bal Sagoth:

http://www.bal-sagoth.freeserve.co.uk/glossary.html

and Byron (vocals + lyrics) also has some parts of their "world" transferred into pictures etc:
http://www.bal-sagoth.net/
http://byronbalsagoth.wordpress.com/the-lexicon/
http://byronbalsagoth.wordpress.com/band-news/

I guess my question is a little foolish, they're a little more like Coheed & Cambria, with all their albums describing one fantasy universe, and all the songs being somewhat thematically entangled?

since I know C and C only by their name I can't really tell you. All I can say is: listen to Bal Sagoth, they are unique and absolutely awesome (the only exception for me being their debut but since "Starfire..." they only released fantastic works)

Skullview do this with their first three albums (The Gleam of the Skull). The first part is quite enjoyable, the other two are decent.

Leviathan did this with the 'Blood Red and True' songs.
Also, Engorged has made 'Death Metal Attack' 1-3.
Know more but I can't think of them at the moment.

Amon Amarth has done Hermod's Ride to Hel - Loke's Treachery Part I, off With Oden on Our Side, then Töck's Taunt - Loke's Treachery Part II off Surtur Rising.

Earliest example I can think of is Overkill, Overkill II (The Nightmare Continues), and Overkill III (Under the Influence) off Overkill's first three full lengths.

Not really a matter of "Part 1, Part 2, etc." but I have the distinctive feeling that The Angelic Process have something going on with their songs that start with "Mouvement". A few melodic and rhythmic lines are repeated on a few of those songs that appear on different albums, like a recurring pattern. My guess is that all the "parts" are meant to be somehow related.

Don't forget Overkill IV (Evil Never Dies) and Overkill V (The Brand)

man, I've had Töck's Taunt stuck in my head for a week, dunno why I didn't think of that one.

supposedly E.vil N.ever D.ies off Years of Decay is part IV of Overkill, part V not appearing until immortalis

Well, I stopped listening after Under the Influence.

Years Of Decay rules. Missing out, man.