I liked this a lot, for pretty much all the reasons the previous reviewer disliked it, so your response to it will probably depend on how you peg your own tastes between the two perspectives.
It's anything but a slam-bang action story. It is, in every sense, an existential novel, about how to live in good faith in an utterly indifferent universe. If you're already recoiling, this is not the book for you. If you're intrigued, it's strongly recommended as a book which uses what's still an original SF idea to make an important point - and make it more effectively than mainstream novels could ever do. The plot isn't full of incident, but that's because the narrative is used to reflect and develop the ideas and characters in an unified manner. The characterisation is vivid and well-drawn, particularly in the context of SF of this vintage. On which point, the previous reviewer found this book dated. I felt the decision to set it in the year of publication (1959) was an effective way to prevent it from dating; the characters and technological speculation are of their time, so anachronisms don't get in the way of the themes, which are as relevant now as they were then. And the last chapter isn't a bit of tagged-on pulp action, but a sting in the tail which sharpens and clarifies everything that's come before.
It's not perfect: it does drag in places, and bits of the dialogue are overly theatrical. But for the most part it's a novel of great ambition which is largely realised, and, in its deep and unflinching look at human nature, a remarkable achievement from an author who was still in his late twenties when he wrote it. It sees SF as a genre capable of more than providing entertaining diversions (not that there's anything wrong with that) and is a highly honourable precursor of much of the good stuff to emerge from and follow the "New Wave" SF of the sixties.