Couple of very cool examples of recurring motifs in death metal come from Asphyx
(intro to the The Rack and the title track) and Sinister
(intro to the album Hate and the track Awaiting the Absu). Both times the intros present a portion of a thought then repeats that thought later in the album within a different context.
Motivic writing is a big part of metal. Sometimes its a very definite part of the writing process (Therion
's Beyond Sanctorum - listen to the way new riffs are almost always a variation of a preceding riff) other times its implied by the similarity of riffs and tonal pallette a band/album uses (Discharge
are good examples of this, but you can also hear it in Slayer
, Malevolent Creation
and tons of other bands). One other explicit example of motivic metal is Aisling Dhorcha by Beithíoch
(main theme occurs in the intro, then the first and last metal tracks are built around it).
The best metal writing like classical is prismatic: it presents several views of similar or the same ideas to create a sophisticated sense of interconnectedness to the whole. Philosophical implications abound.