I love this book.
Not nearly as many grammatical or spelling errors as some of the larger previous releases (which is a nice boon), and the information contained therein is exactly what I was hoping to see develop in a post-Jihad BattleTech "Universe."
I can already tell how the so-called "cut down" is shaping up, and how it will more or less be "glossed over" to make way for a post-Dark Age most BattleTech players will enjoy/be familiar with. Art-wise, the book is relatively uninspired, but the Plog illustrations are very well done, and showcase some great Republic-oriented artwork.
As for the full color maps, well they're just fantastic. As is the Rules Annex. Already mentioned are some forthcoming interim period products geared towards fleshing out the later half of the 31st century, while providing players and gamemasters with some useful hold over information (Read: C-Bill conversion for example. Highly informative IMO.)
Overall, I enjoyed the Republic of the Sphere section. Reading how certain facets of the Republic were formed was fun when you consider that most of the information detailing the Republic comes from Dark Age novels that paint a picture of a fully formed nation. Also of interesting note was learning the final dispositions of the various units of the Inner Sphere, Periphery and Clans. While not an exhaustive picture (in particular, the Mercenary section was a little light), the faction overviews were very well done.
Two Thumbs Up.
Edit: The only piece of art I wish was in the book, was the old school FM color sections showcasing uniforms and paint schemes. That was one of the best parts of the old FM series was seeing uniforms and color schemes coming to life. Really wish CGL would have brought that back for the RAF.