It's a little problematic to put together a compilation of such an album-oriented artist.
But unless you're very deeply into the Leon Russell catalog, this two-CD, 40-track best-of will serve as a retrospective of all that you need, largely covering his work from the first half of the '70s (a couple of songs from his 1992 Virgin album are also included) and featuring his best-known hits, big and small.
It's a well-done tour through his blend of swamp rock, gospel, and bits of blues and country, with material from eight of his Shelter LPs, including the one he recorded in 1969 as part of the Asylum Choir.
Interesting rarities include a 1974 single of "Wild Horses," a 1970 cover of Dylan's "She Belongs to Me" that only showed up on a compilation, and a folk-rockish 1965 single for Dot.