As many of the reviews here point out, this book omits some unpublished poems that were included in earlier editions, which seems puzzling.
Still, this is a wonderful book. It contains all four or Larkin's published books plus other one-offs published in magazines and newspapers.
If, like me, you are coming to this without knowling much about poetry or what 'good' and 'bad' poetry are like, there cannot be a better place to start than this book. You can skip the poems from Larkin's first book, The North Ship, since this was published in his early 20s when he had yet to find his true style and maturity. They are are actually a good illustration of bad poems - exaggerated, artificial emotion, a self-consciously dramatic 'poetic' style, and opaque meanings.
The other poems are brilliant. That nearly all Larkin's poems can fit into a book hardly 200 pages long shows what exceptional quality control he had. There's hardly a duff note here, once you move past the North Ship and into The Less Deceived. I am constantly moved at his skill in pin-pointing a fleeting feeling and putting it into crystal-clear poetry. The themes appeal to me to - love and nostaligia, resentment at obligations to others, wonder at the natural world, the seasons.
Overall, Larkin is arguably the most popular, best and most accessible British poet of the last 100 years. Start here, if you're new to this, and you'll find you stay here a long, long time.