"Every Day" was released as the lead single from the album on 15 October 2012; the song has charted in Belgium and the Netherlands.

[2] AllMusic's David Jeffries said that both the "electronica elite and sweaty club kids" will enjoy a record that "neither challenges nor fades into the background but entices and pleases the whole way through", concluding that: "Opus, the album, is keenly constructed and an excellent beginning-to-end journey in spite of its size.

"[3] Andrew Unterberger of Spin wrote that "even haters will have to acknowledge Opus as being undeniable for what it is, an iconic collection of 21st-century house music that's so expansive and far-reaching it outgrows its very genre, unable to be contained within any four-walled enclosure.

It’s also the best traditional EDM record you've ever heard, not least because it holds up for two fucking hours but it's also a hell of a simulated rave for your airbuds, a window to the boundless paradise of desk-chair dancing and not caring how stupid your co-workers think you look.

[7][8] The CD version is split across two discs, with 10 tracks on the first (ending with "Eclipse"), and nine on the second (beginning with "Sunset at Café Mambo").