Kenny G had a hits collection in 1997, spanning 17 songs and perfectly capturing the time when the smooth jazz saxophonist was one of the most reliable hitmakers in mainstream pop.
Released in 2003, Ultimate Kenny G covers more territory, including two previously unreleased tracks (one being a cover of "My Heart Will Go On"), which does not necessarily mean that it's a superior collection, particularly because the albums he released since 1997 didn't quite qualify as big hits or as his best material.
This gives the album a slightly stronger MOR bent -- which, of course, is remarkable, since Kenny G has always traveled in the middle of the road, but the emphasis on covers ("The Girl from Ipanema," "What a Wonderful World," "The Look of Love," "The Wedding Song") emphasizes this strain in his music; plus, the newer numbers are slicker and more polished than before.
This is a small matter, since most of the collection is given over to his biggest songs, but it is enough to recommend Greatest Hits over this collection, even if this will likely satisfy the needs of most casual listeners.