I know I'm in a minority on this, but I prefer this book to Ariel. There is always something rather touching about early promise: this was the only volume of Plath's poetry published before her death in 1963 and she was disappointed by its reception, and ultimately by the book itself. (She had been writing towards it since her days at Smith College in the early 1950's.)
Brilliant as parts of Ariel were, I find the book as a whole too much; too fragmented and shrill. And I can never separate the poems from the tragic story of Plath's final months.
The Colossus always reminds me that Plath was once a living, breathing, labouring writer: not a myth. The poet of Ariel seems to belong to today's world of distorted and often pointless celebrity. The poet of The Colossus belongs to another age: before conspiracy theories, the man on the moon, The Beatles, the collapse of the Soviet Union. If it lacks the genius of much of Ariel, it has its own strengths. As Bernard Bergonzi wrote in a review in The Guardian: "It shows what a remarkable talent she already possessed and is a very satisfying volume in its own right."