I have a pretty good handle on what makes this one work for me, and it’s tied into why I don’t like any of the recordings I have. It’s a little hard to find a performance that’s done in a flowing style, because most of the choirs I’ve seen are taking care to be precise, take it too fast, or have a wretched canned soft rock beat. You can dig up a decent boy choir or SATB version, such as the St. Phillips Boy Choir (aka Libera).
This is all about suspensions. Going by the melody itself you hardly need to change chords at all–“For the beauty of the earth; for the beauty of the skies; for the love which from our” all fit on the tonic chord. But instead Rutter defines chords with a descending figure over a root pedal point: I – V/I – IV/I – I, putting a suspension decoration on the last I. Then in the two repetitions of the phrase “Over and around us lies,” the melody is a figure on major seconds that must inevitably suspend against any given triad.
In the chorus, “Lord of all, to thee”, on “thee”, we go from a I chord to a suspended I chord (dominant 9 with a suspended 4), to an inverted IV with a suspended 2. The final phrase, “This our joyful hymn,” is a 4-3 suspension, a step on the root, and a 6-5 suspension, all over a second inversion I chord that resolves to a Vsus4, then to a Isus2 and back into his descending figure over a pedal point.
He just never lets you enjoy a simple chord without overlaying either its predecessor or its successor. That works with the legato melody, the sequentially arpeggiated accompaniment, and sustained harmony lines to establish a continuous smooth flow. So the secret here is that it isn’t the melody but the arrangement that makes this one.