Upon its release, Love Letter received positive reviews from most music critics, who complimented its classically minded style and praised Kelly for his singing and songwriting.

[1][2] Kelly was heavily inspired by such soul artists as Marvin Gaye, Jackie Wilson, Donny Hathaway, Sam Cooke, Michael Jackson, and Stevie Wonder.

[16] AllMusic writer Andy Kellman called it "easily the least sexually charged album in [Kelly's] discography, ideal for those who admire him as a singer, arranger, and producer but tune out the fantastical come-ons".

[1] Los Angeles Times writer August Brown complimented its "slow-simmered, grown-man emoting" and Kelly's "melodicism and vocal powers".

[12] Mikael Wood of The Village Voice called it a "commitment-pimping [...] classically minded r&b album" and commented that "much of which plays like a modest about-face from Untitled's unabashed raunch".

[18] Maura Johnston of Spin praised Kelly's "exquisite phrasing and unparalleled ability to belt", commenting that "his decision to ditch the club and retreat to a more conventionally romantic setting allows him to let his voice take center stage".

[15] Ken Capobianco of The Boston Globe called the album "a back-to-basics collection of beautifully sung and arranged tracks emphasizing romance and devotion", writing that its music "complements Kelly’s vocal flights and impeccable, expressive phrasing".

[20] Rolling Stone observed a "relatively novel concept", but commented that "it's a testament to Kelly's ingenuity as a singer and songwriter that Love Letter doesn't fizzle — even with the fly zipped up on his wildest eccentricities".

[13] Hugh Montgomery of The Observer wrote that "It's pastiche, certainly, but Kelly's expressive croon carries the day: equal parts honeyed and rasping, and bristling with a sincerity that reaches its zenith on the spine-tingling, a cappella finale of 'When a Woman Loves'".