At first glance, this mission seems ridiculous and the power weapons laying everywhere can be intimidating, but it's actually quite quick and straightforward and I'll tell you how.
I'll be referring to various points by letter. Each letter is a specific location on the map indicated in the below image:
Before you ever loadout the mission, pickup the Overshield Armor Ability and, if you aren't concerned with saving Credits, snag a Sniper Rifle or Rocket Launcher of choice (if you can't, there is a sniper next to point Point D and Rockets next to Point A that you have time to grab before the assault begins.)
As soon as the mission begins grab your weapons if necessary and jump on the turret that you spawn next to and destroy the explosive barrels at Point E. As soon as Kwon stops talking, multiple portals will begin opening up to your North. The turret can't overheat, so never let up on firing. Focus on taking out Knights first as a single grenade can wreck this entire strategy. After a minute, another portal will open to your West and portals will continue to open here and further south below your screen as well as continuing to your north. Just keep focusing on taking them out until Kwon begins to speak again.
At this point, two small waves of Covenant Unggoy and Kig-Yar will attack. The first wave will come from the South-East between Points C and D (You can blind fire this region and take all of them out before the second wave appears) and the second will be dropped off from a Spirit to the North-East between Points B and C. Stay on the turret and continue to kill until Kwon tells you to destroy the Shade Turrets. At this point, you want to focus your turret fire precisely at where Point is is on the map. The Sangheili that spawn do have a limited count and you can take them out if you prefer, but focusing your fire at that point will destroy the Turret. You'll hear a small explosion and will know it worked when portals begin dropping Unggoy and Kig-Yar to your north. At this point, focus fire right where Point B is placed, but mind the grunts lobbing grenades as well. Again, you'll hear a small explosion and enemies will begin spawning to your South-East. Focus your fire on Point C and you will eventually take out the third Shade Turret, changing your objective to killing the rest of the Covenant forces. This last wave includes Jiralhanae Chieftains with hammers and sometimes you can take them out from the turret, but you may have to dismount for the last couple enemies, hence the Sniper Rifle or Rockets for taking them out from a distance.
Once all the enemies are dead, you're going to switch to the Turret located at Point D. Most of the enemies will spawn to the East. This group includes Unggoy Generals with grenades, Sangheili Zealots with Laser Rifles, and Knight Battlewagons with Scattershots. Knights like to warp and get up in your face, so make them your first priority with the Laser Rifle Sangheili being your second. From time to time, you will see Kamikaze Unggoy running from the North-West to damage your Hornet. They take priority over everything else. Point E is an opening between your hornet and the Wall that can be used to take them out. Just be careful not to shoot your hornet in the process.
At this point, you just want to keep alive and keep the enemy at Bay. Watch your turrets health and if it reaches the red, dismount and try not to be between them and the Hornet as stray fire will wreck it. If your shield gets low, active your overshield ability and try to down as many large threats as possible. Kill enough of them and the next portion of the level will start, with numerous Crawlers and Knights chasing the other Spartan as he attempts to board the Hornet. Stay to the south of the Hornet and try to snipe any Knights or Crawlers you can pick off without taking damage, than board the Hornet when it tell you to and the mission will end.
Simple stuff. Took me forever to figure out on the W8 version of the game, but once I had the strategy, I was able to finish the WP version on my second attempt.)