I mean as far as your grocery store light-reading goes. Suprisingly it isn't the Master Chief bits I enjoyed reading the most but all the space battle stuff. As far as action scenes go, the book has some well written ones, but it always seemed like the ground-pounding segments lacked or even actively omitted things to keep the pace quick. This was a contrast to the space battles which were pretty meticulous.
All in all it added a lot of depth to the Captain Keyes and Cortana characters. It also adds depth to Master Chief that doesnt exist in the Halo games, and thats a shame, cause now there's a huge disconnect between the two different representations of the character.
Thankfully they pooped out a book covering Halo 1, so I dont have to play through it again ha ha ha, well maybe someday... I also picked up Ghosts of Onyx at the grocery store today to read when I finish The Flood and First Strike. Each book is only 350 pages or so, doesnt take long to plow through them.
