[Kallor] writes music of unaffected emotional directness. Leavened with flashes of oddball humor, his works succeed in drawing in the listener - not as consumer or worshipful celebrant, but in a spirit of easygoing camaraderie.
— The New York Times

I can’t think of a better opera [than Kallor’s “The Tell-Tale Heart”] to become a new Halloween tradition.
— NY Observer

Amid Kallor’s jazz-inflected sound world, a lyrical grace threaded through the five cohesive movements [of “Some Not Too Distant Tomorrow”]. The music seemed to distill complex ruminations into a clear vision… Floating, sunkissed passages swam with underlying tension… The final movement left the audience with a peaceful atmosphere, weaving an elegant veil of serene tones – a satisfying nexus between social conflict and art.
— Strings Magazine

The main event was the world premiere of “Some Not Too Distant Tomorrow,” a piano quintet conceived as a tribute to Martin Luther King Jr. With the composer at the piano, the quartet dug into the first movement, ‘The Fierce Urgency of Now’, its angularity and syncopations reflecting the strength in King’s ‘I Have a Dream’ speech. Later came blues-infused melodies floating over alluring pizzicato ostinatos alternating with bristling, rapid energy. The fifth movement, which gives the work its title, comes from King’s 1963 ‘Letter from a Birmingham Jail’, and in its granitic, complex chords, left a mood of optimism in its wake.
— The Strad

[“Some Not Too Distant Tomorrow”] incorporates modern melodic and jazz ideas in a flawless fusion of sounds, reflecting the tension, unease and tragedy of Dr. King’s too-brief life… The slow final movement was the best of all. Here, slow, hypnotic chords and gentle string melodies forged a gentle, hopeful cloak of sound, a light and transparent comfort in these dark times.
— Superconductor

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Kallor’s vocal writing was refreshingly gracious and intelligible, allowing… moments of lyricism, as well as providing hints for dramatic emphasis.
— Opera News

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Kallor’s and Zabala’s magical performance shrunk the hall to the size of an intimate club… The highlight of the evening was the final section, “Exhilaration,” a song-cycle of nine poems by Emily Dickinson. The duo performed them without pause, and their delivery was spectacular… This provided a mesmerizing conclusion to a concert where everything the performers touched turned into gold.
— ClevelandClassical

“Undercurrent,” composed by Gregg Kallor in 2013, was an enjoyable piece in three movements that by turns evoke bustling urbanism, songlike lyricism, and, in the finale, dancing cheerfulness.
— Pasatiempo (The New Mexican)

[Kallor] mesmerizes until he terrifies.
— Berkshire Fine Arts