Slide Jump when possible and stroll on by.
Turn on VISR when you drop down. There are three Stalker Brutes at the end of the first hall. Grab any Fire Bombs dropped. Carbine is very useful so pick it up if you haven't already. It is found to the right after the dark hallway. From here on out, just quickly kill any enemies.
More walking. If you have collected all the audio logs, you do not fight the Drones that come out the door after you drop down. Otherwise, you will be alone and have to fight them. Fighting the Brutes isn't really necessary as long as you have at least one Spike Grenade for the next room. Make your way right and straight down. When you approach the final room with a bunch of enemies, stick the Brute with a Fire Bomb/Spike/Plasma, shoot the Jackals preferably with SMG or Plasma Rifle, and nade the Drones if they are grouped up.
After meeting Dare, make a right after the halls and continue down. Go down the shaft at the end of Sublevel 9 on your right. Pick up a Brute Shot and continue down up to the elevator. Pick up a Beam Rifle on the way before the bridge.
This section has a bunch of Drones coming out of their hives. A Brute Shot can take them all out if grouped together. There are two pathways but will take you to sublevel 12. Right before you drop down, pull out the Beam Rifle and snipe one of the Brutes, then go for the headshot on the Chieftain.
It's best to have a Beam Rifle for the Jetpack Brutes right above you, then go to the left with a Hammer and where the Brute drops out use it, and vice versa. Meet with Buck and go out through one of the doors next to the weapons containers. Don't shoot the Drones when you drop down, then all you do is wait until Virgil opens the door, and head for the elevator.