It's funny, I actually got a lot out of MGSV by doing the opposite. When doing the side objectives, I gained a lot more appreciation for the number of different ways each mission can play out. When playing through each story mission once or maybe twice the first time (when you're limited by what gear you have at that point in the story), you don't really get to see the full scope of the missions.
After doing the tasks and seeing all of the machinations in play and all of the ways the mission could be completed, that would give me ideas to come up with a plan for S-ranking the mission. It was surprising when I realized that this scratched many of the same itches that the Hitman games do, when going for Silent Assassin ranking (for different reasons, obviously; here it's more about being quick and efficient rather than being quiet and not leaving a trace). Doing the secondary tasks with upgraded gear and whatnot allowed me to essentially "rehearse" for the perfect S-rank run. It's led to a lot of "Hey, maybe I can do this..." moments that feel really rewarding when they work out.
I think it's really cool that taking the opposite approach seems to scratch that Goldeneye itch for others. In all honesty, I was pretty positive overall towards MGSV at the time that I finished the main story, in spite of all of its shortcomings. But it's gone way up in my eyes since I've gone back and replayed the main missions for completion/S-ranks. There's so much more there than I was initially giving it credit for.