I respect you for sticking with the franchise. MCC was rough around the edges because of 343 implementation issues, but I had a lot of fun with friends playing through the classic gameplay that had been absent.
All 343 had to do was just ... keep doing what Bungie did. Like Nintendo doesn't drastically alter what 3D Mario games play like. Apple doesn't drastically alter the iPhone each year. Just because you didn't massively change the formula doesn't always mean you're lazy, it often means you've identified a great product and have refined it. Some times you refine it more than other times. And that's okay.
They just wanted so badly to make Halo their own game. And by that point, it simply was not possible. Halo was too massive an IP.
While there's no correct answer here, I think the most widely beloved OSTs of all time probably belong to the Final Fantasy, Donkey Kong, Legend of Zelda, and Super Mario IPs.