The instrumental rock EP was released digitally as well as on CD and an exclusive ocean blue vinyl pressing for Record Store Day.

[4] Brave Words & Bloody Knuckles's Nick Balazs calls the EP "more musically interesting than what his main band has done on their recent studio efforts", noting that on Metallica's records "Hammett's solos have been a point of criticism" but here "those criticisms will be put to bed as Portals shows a talented guitarist utilizing different effects and inspired sounds to create a diverse EP with much replay value."

"None of the tracks sound like unused Metallica demos, nor do they bleed together in a brain-melting patchwork of sweep picking and speed runs", instead "showcas[ing] the compositional and technical strengths of one of heavy metal's most influential and visionary guitarists.

"[6] Pitchfork's Jason P. Woodbury says the EP "reveals Hammett's aspirations to be a film composer, layering crescendoing horns, flamenco interludes, swelling strings—and, naturally, oversized riffs and unhinged shredding—into compositions that could accompany zombie westerns, gothic giallo thrillers, or apocalyptic sci-fi".

"[7] Wall of Sound suggests that the EP is "well worth checking out" for those who enjoy instrumental albums, and while it "probably won't hold the attention of most Metallica fans, it is a rewarding sonic experience that I will be returning to when the mood strikes.