I've lived in Oxford for several years and this book has told me things I didn't already know (unlike just about every other guide book on Oxford I've tried). The way it's laid out into walks (which is how you explore cities) is really helpful too.
I usually get DK Eyewitness Travel but they only have Britain not just Oxford where I will be for a month. Insitight has almost no maps and is organized by trips, not topic so I had to flip back and forth to locate topics. I thought the descriptions were very good, so I gave Insight a 4 rather than a 3 which I was tempted to do in my frustration. Insight is for those who want excursions organized by routes rather than topics.