I enjoyed Fall of Reach. There are a few parts that made me cringe because of how obvious the plot point was in the development of the characters but the space battles and the history of the Spartans and other major characters (Cortana) kept me interested. I started First Strike tonight.
I agree, the biggest fault with the books is how predictable a lot of it can be. Nothing is more predictable than The Flood since IVE PLAYED HALO lol

He writes really fun space battles tho, I agree. Plus like you say the Cortana stuff adds a lot of context to the Halo games that kinda makes a lot of other things make sense.
There's still a few disconnects between Fall of Reach and Halo (game) in terms of how the Pillar's MAC GUN is still working in the game when its demagnetized in the book and how Cortana claims to have knocked out a bunch of ships with the cannon and its like WHAT CANNON IT BE BUSTED!!!!!!!!!!!!!!!!!!!!!
Anyway, thats just the fanboy in me talking.