The latest Halo novel from Thor Books has been released in stores this week. Halo: Evolutions is a collection of stories from multiple perspectives within the Halo universe. The book features multiple authors, such as Eric Nylund, Tobias Buckell, Karen Traviss and several more.
The one thing Halo 2 and Halo 3 did horribly wrong was the story. Rather, the lack of story. The Halo novels, for the most part, fill you in on what has been going on in the Halo universe. The books have covered very important things such as how the Covenant wars started in the first place and how the SPARTAN IIs were created.
The books really do a great job at getting you sucked into the Haloverse. I highly recommend that any Halo fan should at least read the first Halo novel, The Fall of Reach. If that doesn't do it for you, then I don't know, go play Modern Warfare II or something.