It really is a mile wide, but it doesn't have to be an inch deep. However, it shines mostly as a rich sandbox experience. If you go into it just for the main questline, I'm not sure you would enjoy it. You would be overwhelmed with systems and mechanics that you never use. But if you enjoy sandboxes, you'll likely use them all.I haven't played NMS. Every time I look at it, it seems intriguing, but smacks as something a mile wide and an inch deep as far as mechanics and exploration, so I've avoided it.
If you like complex economies, building purpose-driven bases, plentiful reasons to explore, and basically running a space-based business, including recruiting a wide range of ships for your fleet--and much more--then you will enjoy the game. But that is all sandbox. You don't have to do any of it, and if you aren't a sandbox player, you probably won't.
One of my favorite side things was becoming the mayor of a colony on my home planet and having them plot to overthrow, or even assassinate, me as I continuously sent them on dangerous missions. But that, too, is sandbox. People who don't do well with sandboxes likely won't even realize that's in the game.
So yes, it's many miles wide, and if you are an RPG or shooter person, it's going to feel an inch deep. But if you are a sandbox player, it's one of the richest toolboxes ever made.