I'm liking Zoo's storyline, I have a few ways we can clean it up:
First, are you on your way to battle, or on a space station? I think you ought to be a soldier on the space station, which was been under attack. Why? The station was an important defensive outpost near Earth. The attack succeeded and you were hit by the bio-weapon, and few people survived, the rest are zombies. The enemy also hacked your computer and it has been trying to finish destroying the survivors, taking control of multiple dangerous military experiments that were on-board, such as the Mole and the giant demon thing.
This being the case there ought to be other survivors, and where there's still working equipment, you can contact people outside. Destroying the space station and evil AI and escaping are the two main goals.
At some point I threw out an idea about airlocks, and related puzzles...
[EDIT]: Airlocks:
When an airlock is open, you are automatically pulled along the shortest path to an opening. You will constantly lose health from suffocation. If there is no path you must be in a safely sealed area! The solution? Be careful what doors you open without closing the outside openings that lead into space. You can use the doors to your advantage too by closing off an area and opening an airlock to kill zombies there. Heck, you could almost make a whole new game with this. Or a cool puzzle related boss battle.