Let me ask this question, since I have yet to read either "Ascension" or "Retribution" yet:
Was the character Nick always this much of a sh*thead?
He started like one. Our first introduction to Nick in Ascension was of him bullying Gillian so much that she became so upset she created a Singularity and nearly trashed the entire dining hall of Grissom Academy. Then again, he was 12.
He got better in Retribution.
Anyway, about Dietz... this is a serious fall from grace from him.
Halo: The Flood was a much better read than this. To people who say "The Flood" was terrible; it wasn't. At the time that novel came out, it was only the 2nd Halo novel to be created, and reaction to it was mixed, but not universally negative. People were simply disappointed that it wasn't Eric Nylund who had written the book (Fall of Reach is still regarded today as one of the best video game novels ever).
However, "The Flood" was not a bad book. Disappointing perhaps, but not objectively bad. Dietz really got to show off his military knowledge in the writing, and he was very consistent in sticking to Halo lore. Hell, he practically invented the Elites' naming conventions that every author afterward would end up using! He expanded on the ODSTs when they had just been a throwaway line in Fall of Reach and turned them into the ultra-badass "Starship Troopers raining from space" that we're now familiar with them as. He expanded Corporal Jenkins' (yeah, Halo had a CPL Jenkins waaay before Mass Effect did) "death" a lot and turned him into more than a faceless grunt.
The writing had far less passive voice than this abomination of a ME novel. It was simply hampered by the fact that it was a novelization of an FPS, so yeah, it's not going to be great.
Here is a 2008 interview with him. You can see how passionate he was about the Halo universe, to the point where he bought an Xbox just to play the game.
Unfortunately, his writing career in recent years has been declining. His Resistance: Fall of Man novels were not that great either, and judging from what I see, it seems he simply doesn't care enough to play the games he's writing for these days. Shame.