So, what is Post-Rock?

Post-rock is a subgenre of rock music characterized by the influence and use of instruments commonly associated with rock, but using rhythms and "guitars as facilitators of timbre and textures" not traditionally found in rock. Post-rock musicians typically produce instrumental music.
Don Caballero and Tortoise were among the more prominent bands described as post-rock in the 1990s, but their styles are very different, despite being instrumental bands centered on guitars and drums. As such, the term has been the subject of backlash from listeners and artists alike.
Although firmly rooted in the indie or underground scene of the 1980s and early '90s, post-rock's style often bears little resemblance musically to that of contemporary indie rock.

Musical characteristics
The post-rock sound incorporates characteristics from a variety of musical genres, including ambient, jazz, electronica, and experimental. Early post-rock groups also often exhibited strong influence from the krautrock of the '70s, particularly borrowing elements of "motorik", the characteristic krautrock rhythm.
Post-rock compositions often make use of repetition of musical motifs and subtle changes with an extremely wide range of dynamics. In some respects, this is similar to the music of Steve Reich, Philip Glass, and Brian Eno, pioneers of minimalism. Typically, post-rock pieces are lengthy and instrumental, containing repetitive build-ups of timbre, dynamics and texture.
Vocals are often omitted from post-rock; however, this does not necessarily mean they are absent entirely. When vocals are included, the use is typically non-traditional: some post-rock bands employ vocals as purely instrumental efforts and incidental to the sound, rather than a more traditional use where "clean", easily-interpretable vocals are important for poetic and lyrical meaning. When present, post-rock vocals are often soft or droning and are typically infrequent or present in irregular intervals. Sigur Rós, a band known for their distinctive vocals, fabricated a language that critics call "Hopelandic" ("Vonlenska" in Icelandic, a term even used by the band), which has been described by the band as "a form of gibberish vocals that fits to the music and acts as another instrument."
However, in lieu of typical rock structures like the verse-chorus form, post-rock groups generally make greater use of soundscapes. As Simon Reynolds states in his "Post-Rock" from Audio Culture, "A band's journey through rock to post-rock usually involves a trajectory from narrative lyrics to stream-of-consciousness to voice-as-texture to purely instrumental music". Reynolds' conclusion defines the sporadic progression from rock, with its field of sound and lyrics to post-rock, where samples are stretched and looped.
Some bands, such as Rachel's and Clogs, combine post-rock with classical music[citation needed], while others such as Godspeed You! Black Emperor and Fly Pan Am are so far removed from popular music in their sparseness of arrangement and use of repetition, that they are frequently compared to minimalism.
Wider experimentation and blending of other genres have recently taken hold in the post-rock scene. Cult of Luna, Isis, Russian Circles and Pelican have fused metal with post-rock styles. The resulting sound has been termed post-metal. More recently, Sludge metal has grown and evolved to include (and in some cases fuse completely with) some elements of post-rock. This second wave of sludge metal has been pioneered by bands such as Giant Squid and Battle of Mice. This new sound is often seen on the label of Neurot Recordings. Similarly, bands such as Altar of Plagues, Lantlôs and Agalloch blend between post-rock and black metal, incorporating elements of the former while primarily using the latter.[36] In some cases, this sort of experimentation and blending has gone beyond the fusion of post-rock with a single genre, as in the case of post-metal, in favor of an even wider embrace of disparate musical influences.