This is the last chapter that you'll see the black markey guy so make sure you've got what weapons and upgrades you want before the final battle. You'll fight the Nemesis boss towards the end, and this can be a fairly lengthy and frustrating battle. Make sure to keep your distance from it when it charges at you, using your glaives power throw and the Spectre to slow it down. After a bit of that, it will charge up with lighting and throw its blade, which you should try your best to dodge. Throw your glaive at its glaive to charge it with lightning, and then hit it to take down its shield. Two hits from this will destroy its shield, and one more will stun it after which you'll have to run and press "B". After the third time you hit it up close, you'll defeat it and be ready to continue to the final chapter.
(The video belongs to BonersGames)
(FYI i used http://www.xbox360achievements.org/game/dark-sector/guide/
credit belongs to wickeddark)