"Underoath's sound has evolved a lot - from metal to emocore to straight-up hardcore." As demonstrated on their first release, Act of Depression, Underoath initially played a combination of hardcore and metalcore mixed with black metal and death metal. The band kept a similar sound on their second album, Cries of the Past, featuring occasional traces of black metal, but the band later moved away from this style to embrace a more melodic-leaning post-hardcore sound. On the follow up release, Underoath stood "at the heavy metal crossroads on The Changing of Times, a hardcore album that parallels classic arena rock." The band experimented with electronic elements, with Casey Boland of Alternative Press noting that the album "was an Olympic pole vault-like leap forward for Underoath," and that the band was "welcoming the process of evolution." He also noted the addition of Aaron Gillespie's clean singing, which offered "a compelling counterpoint and presaged a swarm of bands adopting the sing-scream dichotomy that would become the hallmark of 'screamo.'" Cross Rhythms noted the growing popularity of the band, and described them as playing "an interesting mix of hardcore and indie rock, utilising loops, keyboards, acoustic guitars and melodic vocal harmonies, amongst the onslaught of heavy guitars and screeching hardcore vocals." Underoath underwent an extreme overhaul preceding their fourth release, They're Only Chasing Safety, with Dallas Taylor and Octavio Fernandez leaving the band and Spencer Chamberlain taking over lead vocal duties. This marked a radical shift for Underoath, "as the band ditched its formerly metal leanings for the decidedly friendly confines of screamo," a change with ignited a debate over which was better, "old" or "new" Underoath. A review by Alex Henderson of AllMusic classifies the album under an alternative rock style which could be described as screamo, post-hardcore, or melodic hardcore, and which differed from full-out metalcore. In another review, Andrew Segal of Cross Rhythms described the album as nu metal, and said that, while on the heavier side of the rock scale, the album is well produced and "shows more signs of intelligence than the [nu-metal] genre is often credited with." For their fifth album, Define the Great Line, Underoath abandoned the pop choruses of the previous album and instead demonstrated a heavier and more eclectic style, updating their sound with "weird" time changes and ambient post-metal passages. According to Sputnikmusic, while the album is basically a modern metalcore recording, it