[20][33][30][40] When asked whether The Open Door was thematically different from Fallen, Lee said that Evanescence and music in general is her venue to "purge all of the negative and hard, difficult experiences" throughout her life, and while that is front and center in this album, it comes from a less hopeless attitude and with a more reflective outlook.

[43] The album consists of gothic rock songs with brooding lyrics, Lee's "searing fallen angel" vocals, and "epic melodies", accompanied by pianos, strings and choirs, while "there's no shortage of soaring, dynamic rockers", Richard Harrington of The Washington Post wrote.

[2] Aly Comingore of the Santa Barbara Independent said it is "rich in instrumentation", swelling with "organs, elaborate string arrangements, and lush choral vocals", and driven by Lee's "intense lyrics and classically trained piano skills.

[38] Ann Powers of the Los Angeles Times described the record as a "whorl of personal confession, high theater and head-banging rock" with "youthfully earnest and sometimes obvious" lyrics.

[17] Jon Dolan of Entertainment Weekly felt the music possessed the "same crush of chunka-chunka riffs, moody electronic churn, and Valhalla-bound metal slam" of Fallen, alongside Lee's "strikingly operatic singing".

[47] Jordan Reimer of The Daily Princetonian said "haunting orchestral arrangements and programming" infuse the album, which is thematically defined by "tumultuous relationships and loneliness", while Lee's attitude sounds "more aggressive and less vulnerable than before" and her vocal melodies range from "sublimely minimalist to roaringly operatic.

[51] Album opener "Sweet Sacrifice" contains "rumbling guitars", a string section, and a "layer of programming" alongside Lee's "trademark haunting vocals and dark lyrics", according to IGN.

[54][52][55][56] Lee said the song is about "dealing with someone with an addiction, which is really hard, especially when you love someone", later confirming it was inspired by the end of her relationship with singer Shaun Morgan of rock band Seether.

"[57] Dubbed a "chick anthem" by Lee based on the reception she received from female fans,[58] the song is "a literal snapshot of one's frustration of dealing with the addiction of someone they love", The Washington Post wrote.

[27] The Los Angeles Times described it as a "harrowing account of a stalker and his victim",[17] Entertainment Weekly called it a "crazy" song that "gets inside the mind of a male predator",[44] and Rolling Stone deemed it "seriously disturbed.

[29][2] Incorporating the Lacrimosa sequence of Mozart's Requiem (1791), Lee's favorite piece of music,[2][29] "Lacrymosa" contains electronic backing beats, symphonic string section, heavy guitar and a haunting choir.

[29] In the song, Lee "decries human guidance" with the chorus lines, "All our lives / We've been waiting / For someone to call our leader / All your lies / I'm not believing / Heaven shine a light down on me", according to Christianity Today.

[47] Nick Catucci of New York magazine described the song as an "almost sultry, industrial-inflected entreaty to an absent God, animating the mighty struggle with faith that the religious and lapsed all share.

The final leg of the tour began on October 23, 2007, in Coral Gables, Florida; the band was supported by Sick Puppies and Julien-K, while Shiny Toy Guns made a guest appearance during the December 1, 2007, show at University Park, Pennsylvania.

[44] Lee "isn't just drawn to melodrama; she thrives on it", Blender wrote, and the album is "denser and more scuzzed-up" than Fallen while "amp[ing] everything up to gloriously epic, over-the-top proportions".

[108] Gary Graff of Billboard said The Open Door shows that Lee "was as much a part of Fallen as Moody", and she translates her "heartache into another successful set of melodramatic goth/industrial anthems with touches of prog and even classical".

[50] Spin's Mellisa Maerz regarded it a "post-dysfunctional kiss-off that builds from ethereal Sunday-mass uplift into full-eff-you guitar dirges, revealing an angrier, more self-assured Lee who waxes sardonic but still misses the comfort in being sad".

[111] Reviewing for The New York Times, Kelefa Sanneh wrote that it is "no surprise" that after Moody's departure "Evanescence sounds gloomier and thornier than the old one", with Lee "finally free to be as bombastic as she wants to be", although the album is "less fun".

[55] Sarah Rodman of The Boston Globe found the final track "Good Enough" to be the "lone glimmer in the gloom", adding that "if [the album] featured more open-throated crooning and less teeth-gritting anger it would be a much more interesting record".

[46] St. Louis Post-Dispatch's Sara Berry opined that while the record is "overwhelmingly dark", the band "manages to escape the 'sophomore slump'", complimenting the music and deeming it "an ideal soundtrack for life's moodier moments.

"[112] Nick Catucci of New York magazine remarked that the album "bristles with righteous anger" alongside "meticulously produced arrangements" that echoes Scandinavian art-metal while Lee "whispers and wails with a pain and ambivalence closer in spirit to the blues".

[65] Santa Barbara Independent's Aly Comingore said The Open Door "successfully slammed in the face of [Lee's] disbelievers", and "moved in a direction that is simultaneously new and reminiscent of the potential at which Fallen once hinted.

"[13] Andre Farias of Christianity Today found the album "an extension" of Evanescence's previous work, and complimented Lee's "operatic soprano" and "enigmatic and sinister" way of channeling her frustrations.

[47] Jim Farber of the Daily News commented that the "hybrid" of musical styles "offers a genuine alternative to everything else that's out there" and the "production has more heft than [Fallen's]", but felt the "jerry-built" sound the band used "isn't anything to be admired".

[113] Andy Gill of The Independent criticized the album, opining that the band "never strays outside the short distance from paranoid to apocalyptic, concerns addressed in as bombastic and tune-dodging a manner as possible".

[117] AllMusic's Stephen Thomas Erlewine said that much of The Open Door is "a muddle of affections" and it sonically "captures the Evanescence mythos better and more consistently than the first album – after all, Lee now has no apologies of being the thinking man's nu-metal chick".

"[17] The Sydney Morning Herald felt that the songs are "gloomier than ever" while the album is ambitious, noting "Lacrymosa" as its centerpiece and deeming "Lithium"'s refrain as getting "to the heart of Lee's life story so far".

[107] Edna Gundersen of USA Today rated the album three out four stars, writing, "Less spiritual than Fallen (and in fact downright decadent in spots), Lee's songs dwell in romantic purgatory" and "her operatic wail is lashed to the band's brand of ethereal goth-metal".

[109] Metal Edge regarded the album a "worthy follow-up that carves out its own distinct niche", and "all the requisite Evanescence ingredients are to be found, but this time, they serve up a tasty concoction of a different flavour".

wrote, "not only does The Open Door well and truly wipe the floor with Fallen, it's also a massive creative leap into territory far more epic, exciting and musically fulfilling than its somewhat restrained predecessor", concluding that it "presents a watertight case that Moody buggering off was perhaps the best thing that ever happened to this band.