I have always been a fan of Heinleins work, and this is one of his best. His greatest attribute is the way he brings characters to life, the main character Woodrow Wilson Smith ( Lazurus Long )is a case in point. Basically the story of his life but spanning centuries this is a story beautifully told with moments of joy and sorrow which you get share with him.
Its easy to forget that this is a science fiction book, so well does the story flow.
If you havent read Methuselahs children you probably need to start there as the main characters story begins here.
Read both of these and then go back and get all his other works, if you like these you wont be disappointed.