Fundamental Chess Openings by Van der Sterren isn't deep but has lots and lots of explanation.
It doesn't cover a huge variety of subpar moves either, because no opening book does -- Opening Theory is a kind of science, and it isn't interested in moves that just aren't very to the point.
However, if you know the reasons behind the moves you play and the moves opponents are supposed to make, then you have a good chance of finding out how the move they made fits in with the general theme of the position.
And anyway, every game reaches a point where you're out of theory, and from where on you just need to play chess (find a plan, calculate tactics, etc).
I read that Nunn's opening book just covers openings approved of by grandmasters and the lastest computer research. Only problem is most tournament players won't play those openings.
Modern Chess Openings covers more variations and openings, including some doubious ones. That is closer to want I want, but I want a step further.
I'm looking for a book that only goes 8-13 moves deep per variation, but has many variations. I'm not interested in memorizing 20 moves deep. I just want to see what can happen with different variations, without buying a bunch of single opening books.
What do you recommend?