I loved it! I have it out on loan to a coworker. I actually bought it a year before I read it. Started kind of slow for me, or maybe I just wasn't in the mood for that type of book at the time. Once I got into it though, I LOVED it! It's really about the ethics of our food choices and he follows a food product through the main types of production: mainstream/factory farm, traditional/sustainable farm and wild foraging. Very interesting stuff.
The "grass" thing has to do with the sustainable farm. The farmer he is following makes the point that he is really a "grass farmer" as opposed to a cattle farmer or tomato farmer or whatever. That we have evolved to be dependent upon a grass-based food chain. It makes more sense when you read it lol!
Definitely

and I also liked the follow-up
In Defense of Food which focused more on the health repercussions of food choices.