I played this once, a couple years after it came out. Solid game, albeit the Prometheans falling well short of the Covenant in terms of interest, flair and intimidation (barring the admittedly effective Composer sequence). The gameplay does strike a decent balance between classic Halo style and the newer-at-the-time more frenetic CoD type. (I admit I chuckled in glee throughout the Mantis segment). I also have not played it in years, so who knows how it holds up lol. The story is mostly pretty flat and cliched, but the Cortana arc, with its intentional echoes of IRL dementia, remains one of the most moving plotlines in the series.
I also listened the shit out of this in high school/early college, so I have a strong attachment to it. I'm definitely more positive on Davidge's material than you are, but I can't say for sure why. I think I just dig the textures and rhythmic layering, because while it's definitely a break from the Halo sound, it also doesn't sound a lot like Zimmer, as many may have feared upon seeing an RC-adjacent name on the credits. One of those things where I go "IDK why, I just *like* it!" Jounnochi's music definitely is the best part though. 117 got so many plays from me, and his material brings the nobility and martial tone. Good stuff!
I absolutely buy that he was a partial replacement for Davidge, because I was struck by how I could *immediately* tell who wrote what for most of Vol. 2. I indeed was also struck when playing the game at the chunks of the Davidge album material that was cut short or absent.
That Marty saga sure was a thing. I'm still not sure why Bungie didn't release Music of the Spheres (I've heard it, and it's great stuff), and even if one is sympathetic to him in his sacking, he sure did some dumb stuff later. One thing that got him in trouble was selling Halo music on his Bandcamp, which was a no-no for obvious reasons, and apparently got him a Bungie/Microsoft nastygram. A lot of interesting musical tidbits though, lost now.