I first discovered the music of Eric Whitacre when I was studying tuba at Indiana University and had this vague idea that I might like to be a choral composer. Whitacre is everywhere in the choral world - he's managed to find a fresh, modern choral sound while still writing effective concert pieces that choirs everywhere can sing. I realized after a while that I'd performed some of his band music as an undergrad - the ubiquitous "Ghost Train Triptych" and "Godzilla Eats Las Vegas". Since then I've become familiar with most of his catalogue.
Whitacre's sound is his trademark; he does wonderful things with clusters and beautiful pan-diatonic chords. He is very often imitated by young composers who copy his harmonic tricks. What sets Whitacre apart from his wanna-bes, though, I think, is Whitacre's ability to tell a story; his music flows, rises, falls; it has a natural arc, a sense of inevitability, what Nadia Boulanger called la grande ligne. This is the essence of composition. It's everything. Some people criticize Whitacre for being too sentimental, too commercial, too whatever, but they ignore the fact that he's an absolute master of form. I disagree with those criticisms, by the way, but it doesn't matter: even if you do lack all other compositional skills but can grasp this sense of the big picture, your music will be successful. More on this later.
Here is a video of "Water Night", the first Whitacre piece I heard. I was in my composition teacher's studio and he told me "I can't believe you haven't heard this." Then he played it for me. It was one of those moments that changed the direction of my career, when I realized that if I could ever create something as beautiful as that piece of choral music, I would find the kind of musical fulfillment I'd been searching for. Still working on it.