As far as prog genres go, neo-prog is the most pop friendly and accessible whereas avant-prog is the most convoluted and complex, often too much for the uninitiated to comprehend.

Yeas ago i made a CRAZY COMPLEX PROG list on Rate Your Music.

These include artists and albums that are either musically complex or conceptually so

Some of the craziest most out there bands include Alas, Anglagard, Area, Art Zoyd, Asceta, Birds And Buildings, Cartoon, Circus, Eclectic Maybe Band, Gentle Giant, Gnidrolog, Henry Cow, Island, Kayo Dot, M.I.A., Marsupilami, Mirthrandir, Moving Gelatine Plates, Mr Bungle, Pentwater, Sloche, Thinking Plague, Unexpect, Univers Zero, Ut Gret, Xhohx, Yezda Urfa.

Some more familiar bands had some crazy complex albums: Yes - Tales From Topographic Oceans, Jethro Tull - A Passion Play, King Crimson - Lizard etc

This list needs an update but there are some gems on here.

http://rateyourmusic.com/list/siLLy_puPPy/crazy-complex-prog-rock/1/" rel="nofollow - https://rateyourmusic.com/list/siLLy_puPPy/crazy-complex-prog-rock/1/

Frets N Worries wrote: As someone who is relatively new to prog, and has clung to the massive concept albums, such as TFTO, The Wall, TLLDOB, etc. I'm curious, what are some more giant concept albums such as these, and which are 'the most prog'?

The proggiest album with the biggest concept really has to be all of Magmas albums combined. They're all part of a complete mythology and story, told in a completely invented language (Kobaïan + genre; Zeuhl) and takes place in some distant future universe. Their sort of volcanic Wagnerian/Orff Jazz Rock-Fusion matches their multi movement concept perfectly. And it's the archtypical love/hate-band. I guess the self titled 1970 double album debut, where all these ideas and future ambition of telling this grand apocalyptic story was already in place - must be the proggiest single release "statement" (and the only logical place to start). I googled "Magma band mythology" and the first I found was an attemnt to explain it here at PA fifteen years ago by none other Shakespeare himself:

Here's an excerpt from http://www.progarchives.com/forum/forum_posts.asp?TID=46401" rel="nofollow - "Chronologically, the earliest tale in the Kobaïan anthology is that of a man named Köhntarkösz. Köhntarkösz is an Earthling. We assume that this takes place sometime in the near (or maybe distant) future. One day, by whatever means, Köhntarkösz stumbled upon a long forgot, ancient tomb, belonging to a former Egyptian Emperor. This makes us think that Köhntarkösz was an archeologist, historian, researcher, or perhaps just lucky explorer. At any rate, the tomb belongs to Ëmëhntëht-Rê, who, in his life, sought nothing more than to discover the secrets of eternal life. Ëmëhntëht-Rê came close to accomplishing his goal, but before he completed his task, he was murdered. We’re unsure whether the murder was related to his work: whether an underground organization wanted the secrets of endless life to go unearthed, or if the Emperor’s reign was won by revolt, or if the Emperor just owed somebody a lot of money. Who knows, maybe Ëmëhntëht-Rê fell on the knife.

While inside Ëmëhntëht-Rê’s tomb, Köhntarkösz is met by a startling and vivid vision of the bygone Emperor. It is in this fashion that Ëmëhntëht-Rê’s wealth of knowledge and wisdom, regarding life, death, man, God, time, existence, and eternal life is passed to the humble Köhntarkösz, who now, revealed the truth, sees how evil mankind is, and how imperfect Earth is...and sees a solution. However, I believe that in this moment a prophecy was also made: and it is articulated in the song Ork Alarm. The prophecy is essentially that if ever the secrets and wisdom of Ëmëhntëht-Rê would be harnessed to craft the ideal society; if ever human life was perfected; if indeed the evil of man was surpassed; the People of Ork would come and end it. The People of Ork would destroy all progress. Perhaps the prophecy isn’t an ‘if’ situation: maybe even Köhntarkösz seeing the vision was enough to spit the People or Ork out of their waiting. Maybe from that moment the People of Ork have been on their way (which would mean either they live a couple hundred galaxies over, or their ship runs on diesel.) What is for certain is that the People of Ork will play a large role in the distant future of mankind"

...link to the rest of the text & thread can be found by pressing the linked title. I don't know if this it the best out there, but seems like a good read - and for some reason only links to other PA-pages works for me.

As someone who loves literature and mythology, you have given me a golden opportunity and I thank you very much

Obviously based on the book of revelations, the eclectic nature of this double album is stunning going in psyche, metal, pop, avante directions seemingly all at the same time. Recorded in 1971, the band broke up before it was released going on to become an influential 'cult' album. Bassist and legendary vocalist Demis Roussos mentioned it in interview many years later and was obviously proud of it. Mostly Vangelis masterminded it before he later went on to have the odd dabble or two with a synthesiser. Great drumming and guitar from Lucas Sideras and Silver Koulouris with a side helping of Irene Papas on the 'orgasm song' (actually its about an exorcism!). A wild ride if ever there was one.

It depends on how much you want someone's eyes to glaze over.   A Passion Play comes to mind.

definitely the great classics

1. IQ - "Subterranea" 

2. Spock's Beard - "Snow" 

3. Marillion - "Brave"

4. Saga - "Generation 13"

5. Dream Theater: "Metropolis Pt.2: Scenes From A Memory"

6. Queensrÿche : "Operation: Mindcrime"

Sorry, I was too quick with reading the OP, but your thread title can confuse.

1. The Radio Gnome Invisible trilogy released by Gong in 1973-1974.

2. Every album by Ayreon. Several of the Ayreon albums overlap, and indeed, the name Ayreon is one the characters in the overlapping storyline.

3. Jeff Wayne's The War of the Worlds.

4. Frank Zappa's Joe's Garage

5. Solaris' Marsbéli Krónikák - entirely instrumental album based on Ray Bradbury's The Martian Chronicles

these three definitely are must listen. 

highly recommended! 

IQ - Road Of Bones

You beat me to it! A magnificently crafted concept album.

Very interesting but I think it's also very important to point at the basis for this story which is as the author states:

"The following blog is merely comprised of assumptions, based on the mood and atmosphere of the music, and what little fact I know to be true." 

Ah A Passion Play, my favorite Tull Album

Devin Townsend's Ziltoid the Omniscient

Queensrÿche : "Operation: Mindcrime

One less known but all their albums tell a Sci-Fi story about a galactic war: 

https://1974.bandcamp.com" rel="nofollow - https://1974.bandcamp.com

(The death of the herald is the one I like the most-

I am not sure how to say much about all this. There are things that are (supposedly) BIG, and the contents is like a pulp fiction writer putting together small vignettes. You get the feeling the concept is ... wait a minute ... where? Then you get some things that are intentionally "underwritten" with no obvious idea as a concept and they stand out really well, but unlike many others, they don't go ... look at me, I'm a conceptual star! 

The ones that, at times, confuse me, is where it is all lyrics, and well, novels are like that ... just words, and you create your own mind movie and music ... but while some of them are far out, and very well done, when it gets to the end, you go ... did I read all 1000 pages of that thing? Or did I hear all of that before you decide you like it.

I always thought that things like The Gong Trilogy, was more of a very long story, well thought out for the most part, but difficult to put together as a good conceptual piece ... it still works nicely, but while all three albums were pushed as a part of the whole thing, I'm not sure that you and I can sit down and conceptually devise all the twists and turns of the whole thing, and its many changes, and then, we add the elephant to the discussion ... when it was stated that one album was all totally ripped and stoned ... and it is, conceivably, their very best!

MAGMA, fits somewhere else ... they have, at least, been consistent from the start, and have not really wavered that much from their novel ... it just has no ending, it seems like ... and for many of us, it just keeps getting better. I suppose that some of us think that the different language creates a sort of mythology to our mind and ideas, and some notes here and there suggest this and that is happening ... but you and I are still going ... really? It's still magnificent to listen to, but is that what a concept is supposed to be about?

I much prefer the "non-concept concepts" of some works ... I remember an album from NEKTAR called "Sounds Like This" ... and it was far out ... and then you went to see the band ... there it is ... no lie here, no concept, no ideas ... just the music and the band, and in my funny peanuts like world, that is a fabulous concept ... right up front, true, and visible ... but we would rather consider at least one other album of theirs as more important conceptually because of the lyrics. Although another album, was a bit of an assault, but it seems to have fallen off on the last song, that really, doesn't fit the whole thing, unless the idea is to actually say that we don't want to do this again, or at least one member doesn't, or can't ... anymore.

One of these days, I''ll cut up the idea of "concept" and try to figure out what it might be. I have been told by many that some of the things I write are quite conceptual, but I'm a total intuitive writer, and I don't even know what a concept really is, in my work ... I just keep up with my inner movie ... and am not really interested if someone thinks its this or that ... but it's funny to hear some folks try to break out ideas of a concept ... it tickles me silly and then some!

Camel - The Snow Goose

Three concept albums (and there's no argument that they are) which just happen to be amongst the very best albums ever recorded.

Frets N Worries wrote: Atavachron wrote: It depends on how much you want someone's eyes to glaze over.   A Passion Play comes to mind. Ah A Passion Play, my favorite Tull Album

One of prog's greatest love letters.

Nick Prol & The Proletarians - An Erstwisle Alphabestiary

Available to listen here:  https://proletarians.bandcamp.com/album/an-erstwisle-alphabestiary-book-one" rel="nofollow - https://proletarians.bandcamp.com/album/an-erstwisle-alphabestiary-book-one

So far, only "Book One" has been released. Not sure when "Book Two" will be released.

There is also Sound Horizon's Marchen, a rock opera surrounding German fairytales.

Also, "Tommy" and "Quadraphenia" by the Who have some very progressive elements in use of orchestration etc.

The Similitude of a Dream

Thick as a Brick (Jethro Tull) - Although Ian Anderson always said it was a joke to make fun of concept albums...

Metropolis Part 2 (Dream Theater) - The best of DT and an icon of progressive metal. They have not managed to repeat an album of this nature until today. 

Misplaced Childhood (Marillion)  - Fish's four albums in Marillion are my favourite of the band's, and this album is their flagship, as well as neoprog's.

Tommy (Who) - A very progressive concept album in my opinion, much more so than others considered progressive by definition.

i dont want tospoil the end but i gess  is easy to know