A very active, easy to learn system agaisnt 1.d4 backed up with good theory and advice. Also, they go into very good systems against white's other first moves, except for 1. e4. I've noticed that most 1.d4 players don't bother with main line queens gambits but opt for simple systems like the "Old Man's Bad Habit", Hodgsone tromp, colle, etc. This books deals with all of those and a great section on the Reti. A good repertoire book.