"Ghost Reveries" received widespread acclaim upon release. Thom Jurek of AllMusic cited "Ghost Reveries" as a culmination of everything Opeth had worked towards throughout their career. Jurek defined the album as "fully realized, stunningly beautiful, and emotionally fragmented; it's a terrain where power, tenderness, and sheer grief hold forth under heavy manners. Awesome." "Billboard" described the album as delving further towards Opeth's progressive tendencies, commenting that the "alternating between powerful metal bursts and gauzy atmospheres requires patient listening, but it allows for better exploration of the beautifully dark world Opeth creates." Brandon Stosuy of "Pitchfork" praised Opeth's diverse musical influences and instrumentation, as a blend of "prog, jazz, stoner haze, blues-rock, Indian raga, pastoral tips, and acid-tinged freakers." "Exclaim!" reviewer Max Deneau similarly praised their songwriting and musicianship as key to Opeth's formula, whilst commenting on the addition of keyboardist Per Wiberg as having added "a volatile new dynamic to the band." Keith Bergman of Blabbermouth.net gave the album ten out of ten, one of only 21 albums to achieve a perfect rating from the site. "Decibel" called "Ghost Reveries" "achingly beautiful, sometimes unabashedly brutal, often a combination of both." "The Aquarian Weekly" placed "Ghost Reveries" among the band's finest work, writing: "This record was in the running for best metal release of the year before it even came out and now that it has, it may very well have decimated any competition."