Im a fan of the whole halo series not just the games, so this book was a must for me.
Set before any of the other books or games, in short, the book is based around Sergant Johnson, who is right on the front line of the insurrection, a human civil war. He is then reasigned to the planet Harvest to train recruits. This is then the 1st planet the covenant attack.
It starts slow and you have to stick with it until it picks up pace. When the book gets into it, its an addictive read, and i felt had alot of depth to it, espeically near the end.
Its a great addition to the halo series and its nice to have a good idea of the games or other books as you find out the origin of certain things, but its by no means vital.