I keep forgetting to do anything in the main quest at all. I still have two of the three missions that Sarah gives you after you do her first thing. I've done a bit of the Vanguard stuff. I faffed around on Mars for days. I just finished doing a planetary survey for Constellation that I picked up way back when I was last in the Lodge. I couldn't do it sooner because I lacked the gear to run around semi safely on the planet. During the survey I came across some pirates who were wandering off to explore some bunker so I stole their ship. Who's the pirate now?
What can I say, I'm enjoying it. I think I'm just receptive to the way Bethesda games are designed. Something about them "just works" for me.