THATS MY COOL MAN I CAN'T TAKE IT OFF!
Cortana's easy.
Just whore the shotgun at the start till it runs out of ammo, then swap it for the sword. Use the brute shot for long range encounters to knock spikers from their perch or break the brute flood at long range. Remember to hit tank forms in the mouth then immediately rush backward. Flamethrowers are good short term, just post up someplace where there's only one entrance and make yourself known.
Couple of tips. First, at the pelican area (where you first drop down). You have to get through to the upper area quickly, otherwise infection forms will likely get to the dead marine who's by the rocket launcher. We all know how that goes. Second, in the room where you find the tilt skull. When you first enter, rush the platform, drop a bubble shield, and then go down to the bottom. You can see everything going on above you through glass. Makes that part so much easier.