The classic soundtrack is also a much better improvement.
Not sure I agree with you on that one, actually. I like Marty well enough, but particularly by Halo 3 it seemed like he'd just run out of ideas and was just rehashing or outright re-using tracks from the first two games, though while I didn't really like most of the music in Reach I thought his work on ODST was incredible. A leitmotif or a theme is good, but it was starting to just feel repetitive and uninspired by the end. Not to mention that Halo 4 has one of my favourite soundtracks in any game ever: stuff like 117, Arrival, Faithless, or Green and Blue are all amazing tracks, and do a lot to breathe fresh air into a soundtrack that was starting to go stale.
OT: It's definitely weird seeing Halo 4 like this and comparing it to the sounds I'm used to. The Assault Rifle's definitely much worse sounding here (and I'd actually say its normal Halo 4 sounds are better than the version in Halo 5!), but the Storm Rifle actually sounds powerful with the older sounds rather than the joke that it is, and the Battle Rifle's a lot more menacing with the heavier bullets. That said, while I do actually prefer the older Magnum sound I feel like it doesn't really fit a weapon which can be fired as quickly as Halo 4's own pistol as it's just too heavy to feel natural.