Yes they are actually. It really draws you into the world of halo almost as if it were the game itself. I found it quite accessible for, at the time, I hadn't played the games. It really showed me the scope of the world and familiarized me with the Characters and Enemies.
I would note that if you aren't comfortable with War style fiction and names, it might not be as accessible to a broad genre of readers. However, if you are looking for some true war style sci-fi, read dem books!!