Heinlein is one of my all time favorite, with F. Herbert, J. Vance, P.J. Farmer, and a few others. I trully love 'Stranger in a Strange Land', 'Friday', 'Time Enough for Love', and 'Starship Troopers'. This book doesn't get even close to those.
As far as I'm concerned, the merit of a book can be most safely assessed by asking oneself the question "Had this book been written by a total stranger rather than the Grand Master himself, would it (1) still be in print, and (2) sell as much?" In this case, I think that the answer would be a clear no. The stories are very dated, both in their vision of science and in cultural references (blacks are "negroes", women are treated in a superbly paternalistic way...) The story-telling itself is not up to Heinlein's standard: most of them are half finished at best. Finally, the stories totally lack the humor and wittiness that makes Heinlein such a great author.
I'll grant that this book looks into some serious themes, and fosters reflexion. However, some of the themes are just silly.
'Friday', 'Stranger...', and 'Starship...' are as much if not more thought provoking, and the storytelling is light years better than 'Assignment...'
Overall, I would recommend this book to Heinlein's fans - not to people who do not know his work or enjoy it more casually.