Unfortunately, there are not many opening books with lots of explanations :-(
You may want to check another work of Watson : Mastering Chess Openings vol.2 (1.d4) - it's not a repertoire, but it gives a nice overview of many thematic ideas in a large array of systems
Do you know a book, which is similar to'A Strategic Chess Repertoire for White' by Watson meaning that: it covers similar openings (1.d4 - Queen's Gambit, Slav, Semi-Slav, Indians), is designed for white and focuses on ideas but is (at the same time) less advanced and involves much more explanation and narrative?
(In other words I'm looking for white's equivalent of Soltis' 'Black Defensive System for the Rest of Your Chess Career')