Story-related and cannot be missed. Just travel to Feros and follow the quest objectives.
*** Spoiler - click to reveal ***Here's more detailed walkthrough:
- Tired of fighting Geth? Here's more Geth! Kill all the enemies on your way to Zhu's Hope
- Go through the colony until you meet with Fai Dan. Your chat will be interrupted by, you guessed, more Geth
- Before you are able to progress the story and visit ExoGeni Headquarters, you have to help Zhu's Hope. One objective is mandatory, but there are several assigments you can take from colony's inhabitants - these sub-quests are resolved in the same area
- Once done with helping, go to the elevator and inside Mako. Kill everything that moves until you reach the main building (there's a station mid-way, where you can get additional intel and one assigment)
- The ExoGeni HQ is more or less linear and the only tricky part is when you have to change gate's pressure. Use 17, 11 and 5 buttons, or 13, 11 and 7 for the gate to crush ship's "legs".
- On your way back it's important to visit the station, where you'll get a little help in the form of nerve gas that works as a granade upgrade. Use it to save colonists (melee also works).
- The rest of the mission is pretty much linear and I won't spoil you the details - have fun!