>>361630078
it's an explore game, refining your gameplay to get good and learning it all is the "fun" itself. 

The "priority" story missions are guiding the player onto a smoother difficulty curve so they don't accidentally run straight into the hardest zone and get wrecked over and over. You can literally explore the entire game at the start. You can even clear the end game zone right to the finish if you're good enough, you just won't be able to trigger the final cutscene if you're not also on the final mission.

You'll have a very very fun time trying to do the game without a nice rifle and ammo from the security clearance unlocks though, so maybe do the missions if you're new.