Saving crew members...
Even though the story line of ST:Voy:EF was linear, there were at least two occasions were you (Ensign Alex) could prevent the death of a crew member (even though it didn't have any impact on the story in general).
SPOILER WARNING
The first time is right in the beginning, when you have to activate a forcefield to contain an explosion on board Voyager, as you make your way towards Engineering. If you activate the forcefield too soon, you'll trap the fleeing engineer and he'll die right before your eyes. If you activate it at the right time, you'll save the engineer and yourself. And if you're too late, you'll die.
The survival of the engineer is not necessary for thew story, but optional.
The second time: Les Foster (the leader of the Hazard Team) is abducted by the Borg. You CAN save him during your trip on the Borg Cube (with 7 of 9) if you figure out how to get to Foster in time. It has no impact on the story, but it is one more life saved.
Does anyone know other moments in the game like this? (Where you can do something optional, but which isn't required to finish the game?)