Combining the good features and quality of books like Betrayal with an artwork rich environment that follows in the line of Liber Chaotica, the Emperor's Might is a nice collation of art from across the Warhammer 40,000 Universe that features the Space Marines near exclusively.
The front cover of the book gives away the content: a mixture of both old and new, materials that has been extensively used before, artworks are are relatively new, some that are underused, and some that have never truly seen the light of day. Note also the satin book mark that adds to the quality of the book (visible in the lower left of the first image).
The older artwork that can be found in the book is still interesting. The front cover of Rogue Trader. The covers of very old games such as the second edition of 40k, as well as "space marine" and others.
Newer artwork is in there, below is one such example: the front cover of the Horus Heresy novels (Horus Rising) which features the Luna Wolves Legion.
Finally, there are other bits and pieces that I've never seen in any codex. Sketches of space marines in charcoal or pencil of them looking at ease, in action, and generally portrait shots. These are all excellent insights and makes the book a collector's item for such artwork and one that I can certainly recommend to art enthusiasts.