Upon release of Take That's number one-album, III, "Let in the Sun" was described as the likely second single from the record and a natural progression from the nostalgic and upbeat dance vibe of "These Days".

It was described as a mix between Calvin Harris and Mumford & Sons by critics, with Barlow calling the song a "homage to the early years", and Howard Donald raising the prospect of the band taking the single to Ibiza due to its club sound and music style.

Take That performed the single for the first time as part of a live set for BBC Radio 2 in December 2014.

[2] The single received positive reviews upon release of their UK number 1 album, III with Entertainment Focus calling the single "a nod to Take That's early days with its dance rhythms and uplifting chorus"[3] and The Guardian commenting that "Lyrically it's euphoria with a capital E, Barlow crooning 'Open up, everyone's waiting ... open up your windows and let in the sun' as Edge-style guitars glide epically by.

"[4] RTÉ called the single "a nod to the band's early years of hedonistic party anthems", concluding that "Let in the Sun" is "a straight-up-hands-in-the-air dance floor hit with a huge piano riff that brings in one of the most uplifting choruses on the record.