Awesome game! It's different and varied.
I recommend doing the storyline first and then follow up with the rest of the quests, some require you to be fairly strong (high HP, strength and other skills) in order for them not to be super frustrating by getting killed easily or too often.
Hated Mothership Zeta! The aliens were extremely annoying along with going through the spaceship, which I found to be extremely confusing and extensive!
I'd say this must be in your must play list if you haven't played it yet.