I love the first two Dead Space videogames, and I've finished the main trilogy plus another one released on iOS. This art book contains concept art, drawings and lore about the 3 main titles and bits from two small comic book series.
Essentially, if you liked the games you will enjoy the pictures and the companion text. It tells many small details about most topics, from the whys and hows of the weapons to the suit designs, the different enemies, and of course the markers. It does contain huge spoilers so you should be careful with that, but after beating the games, it is a must read to expand the lore.
To complain about something, that there seems to be more content about the third game than the first two, and at least for me those are the best titles. I'd love to have seen even more about the Ishimura ship... but even with that it is worth it for fans.