Within the genre of Prog a specific characteristic is found which allows for a more or less good delimitation to other musical directions, namely, the manner of composition and in combination the arrangement and the instrumentation.
Prog is by definition the opposite of pure. Usually, within a single song, many sound colors are used which produce a symphonic overall impression. Combined with a melodic and rhythmic countermovement (contrapunkt), an often inextricable network of musical lines is produced for the non-instrumentally trained listener, which he can only consume as a whole.
This results in the already mentioned subjectively perceived "emotional depth" of the music, which also persists with frequent hearing, since the listener always discovers new elements in the sound mesh hidden behind the main melody lines perceived at the first listening, and which, subconsciously for the listener, makes the music interesting and varied by constantly changing the harmonious references within.
As an impressive example of an excellent interplay of instrumentation, arrangement and contrasting counter-movement, I would like to point out "Playing the Game" from Gentle Giants' album "The Power and the Glory". Here this elaborate way of composing, borrowed from classical music, is carried out in an impressive manner. Almost every riff and every small melody of the song resembles fragments of the main themes, and through this self-similarity a formal unity of the composition results, which can be analyzed not only academically, but also fest emotionally.
A comparison of the early Genesis and early Marillion songs is interesting with regard to composition in Prog. Marillion was often referred to as a copy or rebirth of early Genesis. In fact, strong similarities can be identified.
The timbre of singers Gabriel and Fish is quite similar. Both have the ability to change fluently from the normal to the head-voice. Furthermore, both singers tend to pronounce hyperrealistically, with a strong emphasis on pronunciation of the consonants and vocal exaggerations, up to a persiflage (very clearly e.g. in "Get 'em out by Friday" by Genesis and "Assassing" by Marillion). In addition, both bands have a similar basic style with many arpeggios and "keyboard sound layers".
Significant differences arise when looking at the compositions. The music of the early Genesis, on the albums "Nursery Crime" or "Foxtrot", is much more complex in the overall structure as well as in the detail resolution. The above-mentioned stylistic features are almost the tonal ideal of this music. However, out of the possible variety of musical expressions Marillion mainly use those components which could be described as superficial.
"Marillion's Script for a Jester's Tear" is composed, for example, of quite clearly delimited 2 to 4 chord schemes, which are mostly played in the form of arpeggios, sometimes broken into breaks and mostly underlined by keyboard layers of the same Chords. The melodic ideas and harmonies are very appealing and original, but the complexity of the harmony and melody, and the virtuosic dynamic play of the early Genesis are not reached by Marillion even in their best phase.
A piece such as "Seven Stones" by Genesis can only emerge from the individual ideas of the participants through a very intensive exchange of ideas by several musicians / composers, through an ongoing constructive compromise. "Seven Stones" also uses the above-mentioned characteristic styles, but they are much more refined compared to Marillion.
First of all, the overall musical structure is much harder to comprehend because we are not dealing with clearly defined themes and parts, but with a structure in which each theme, each melody line, seems to lead into the next part inevitably. The transitions are so well elaborated, the themes are interlaced so well that no defined beginnings or ends are recognizable and thus the sequence of the piece is hardly foreseeable for the listener. Very long passages of the piece represent a gradual melodic and harmonious metamorphosis, the structure of which is revealed only after repeated listening.
Nevertheless, the complexity is hardly perceptible, always serves the whole and renounces entirely superficial effects. The harmonies have been very versatile and were certainly created in a long development process. All this makes the early Genesis songs so timeless.
I hope that with my remarks I did not irritate the Marillion fan club. I have the first 5 Marillion albums in my collection, and some of the old stuff I like very much still today (Incubus, Emerald Lies), but it does not reach up the ingenious quality of the best songs of Genesis, Yes, Gentle Giant, Jethro Tull. In principle, I would extend the above about Marillion to almost all Neo-Prog bands (like Pendragon, IQ and similar) that are partly praised and critically placed on the same level with bands like Genesis and Yes.
Unfortunately, these bands only offer a reissue of styles established by earlier groups. But for me the originality alone would not justify the above quality differentiation. If there was a band that was stylistically very similar to the early Genesis and their composition had the same quality of the original, I would certainly be one of the first buy the CD.
However, an exact copy of a genuinely progressive composition style cannot exist in principle. A group of composers who would be able to do so would introduce a variety of ideas and expressions that, given the high complexity of the musical material and the variety of degrees of freedom, an exact copy of an existing style would be more than unlikely as a result.
If, on the other hand, you try to duplicate the ideom of a band exactly, it will only work as long as you are moving on the ground already established by this band. No one could tell the copier how a further development of the copied style should look like. If the copier does not leave the established terrain in the long term, one can hardly speak of progressive rock.
Thus the substitute term "Neo-Prog" is negatively affected in certain circles. Examples of bands that have emerged from the shadows of their idols, despite a strong leaning towards established musical ideals, are the Swedish bands Anglagaard and Anecdoten. Anecdoten sound very strong like the King Crimson of the middle seventies and the music of Anglagaard sometimes sounds like an instrumental extract of the early Genesis.
But because each of these ideomas represents an extremely wide and open field of expressive and developmental possibilities, the musical elements can be changed at any moment during composition, and since every human being has its very own character, the development of very complex own compositions will reveal a certain degree of originality inevitably. Thus, the music of talented Prog bands will develop in their own way and soon leave their idols behind as long as the progressive spirit and the necessary creativity can be maintained.