I currently live in Lisbon so I use this guide quite.
Most importantly for a travel guide, it contains no factual innacuracies (or none that I've found yet).
It contains all the information you might possibly need, from transport to places, costs, opening times, maps, and a brief historical/contextual information. It's all presented really well, in a way that is easy to read and browse. You can easily find what you want in 30 seconds, or spend longer reading up on something if you wish.
The pictures are great, the pull out map is excellent and waterproof (Lisbon can be very wet from November to February), and I couldn't possibly ask for anything more from a city guide.