really, once you get past the first boss, you are let off the leash, and while you can repeat the pattern and upgrade again, the game would benefit a lot from telling you this.
Actually you're let off the leash before that. It just doesn't tell you. At all.
It's implied that you can't go anywhere without beating the first boss but...you can explore all of Alpha Sector to your heart's content before that point.
oh, yes, definitely true in the tutorial mode going away. I meant it more from the quest direction side of it. that's the last thing the game tasks you to do, at least until they get past the early beta phase.