As a rule, compilations have two audiences - completists and casual fans. Dylan, the latest in a long line of Bob Dylan compilations, is unique in that it's not for either, but for a semi-casual fan who has all of Dylan's classic albums but doesn't want to filter through, say, Knocked Out Loaded to find the diamonds in the rough.
Across a forty-five year recording career (at the time of release), even at his lowest ebb, Dylan had some amazing songs to dig up. The best thing about this compilation is how for the most part, it avoids the obvious - Highway 61 Revisited, Blonde On Blonde and Bringing It All Back Home, as well as Blood On The Tracks are all under-represented. Instead, we have the single best songs from Dylan's worst periods - 'Brownsville Girl' from his appalling 1980s period; the adorable 'Blood In My Eyes' from his 1990s covers albums; 'Changing Of The Guard' from the unloved Street Legal album; 'Blind Willie McTell,' one of his rarities previously only on the Bootleg Series compilation.
If you have all the classic albums and need to know where to go next, then this is your starting point. Alternatively, if you don't want to explore all of Dylan's catalogue, this will give you a reasonable overview in the meantime. In fact, the album is worth it just for the non-album, Oscar-winning 'Things Have Changed,' only available on previous compilations.