This book is excellent, and needs to be read by any serious scifan. The aliens are original and unique. If you can read this book and not find certain aliens made famous by films from the 70's and 80's then you don't know your sci fi! This book along with Quest for the Future, Slan and The Weapon Shops of Isher are essential and compulsive reading, very hard to put down once you start reading. Van Vogt won few major awards but his sci fi visions are amongst the best and his story teling is fery fluid. I would recommend also the short stories 'The Monster' and 'The Rulers'.