I like to do thorough research before a trip and frequently use the "big" travel books. But unless you're visiting an area for a month there sometimes is more information than you can use. They're also not that portable, which means they're less useful as guides DURING the trip, and sometimes their maps aren't that easy to use.
This guide avoids all those problems. As with all DK Eyewitness travel guides, it's lavishly illustrated with photos, which help you see what places really look like, and it has excellent maps.
It's a perfect "take with" book. We spent 5 days in Vienna recently (stayed a block from St. Stephens, right in the middle of things) and we used this book constantly. Vienna is a wonderful walking city and this book was easy to tote; no travel guide is useful out on the town if you left it in your room. We typically start the day with a general idea where we're headed but like to improvise specific destinations, so we constantly need to check the map and look up attractions. This guide is ideal for that. I had several guides but this wound up being the one I used; it had the best detailed maps and just the right amount of information.