I reformatted before because my computer was dying, but SE ran fine until then... odd...
EDIT: READ THIS:
Ok, here's what I have in plan for this mod. We probably won't get it this advanced, but hopefully close
At the start of the level, you are dropped by a Cov. dropship on the beach. You walk up and discuss the defences on the island with the ranking officer on the beach, a red veteran Elite standing near the 2nd line of defence (near the shields), when all of a sudden you hear a roaring noise as two Pelicans fly over your heads. You see a small, spherical object tumble from the Pelican's rear door and dive...just in time. The vet is not so lucky and is ripped apart from the blast (yes there will be blood and guts

) and you go beserk. Being a Zealot (Gold Spec. Ops. Elite), you whip out your energy sword and charge at the responsible Marine scum. You lunge and impale him with the sword, it goes right through him, and then he falls to the ground with a gaping whole in his chest (mmm...kebabs). This cinematic then fades into gameplay.
Your first objective is to hold the beach against the Marines. This is easier said than done, especially seeing the human apes have the Demon to back them up (yes this is written from a Covenant perspective, I don't hate other people). The Demon will tear through the Grunts and force the first line to fall back (as it does in the original level). From behind the shields, you have to lean out and take potshots at the enemy.
By this stage, Echo 419 will drop off a Warthog behind you, bypassing the 2nd and 3rd lines of defence. The Demon will flip an overturned, badly damaged Ghost and charge past all your forces to the Hog. He will then get in, as well as two Marines, then drive like mad towards the map room. On the way out E419 will be chased by a Banshee, which will then get shot down by the chaingun, adding a bit to the level of chaos
Now you must get to the map room to stop the Demon from accessing it, by the time you get there all the Cov. forces will be massacred with only a few Grunts left cowering behind crates, and a Pelican dropping off more Marines in front, where the overshield is. This will now be a double speed powerup, assisting you in killing the small force of Marines in the area. When you get to the map room door you find it has been locked down, a Zealot peering out from behind the small looking glass. Now you must hunt down and kill the Demon.
By this stage, the Demon will be battling his way to the security room. Run past the few surviving Covenant on the way, run into the storage room, past the two dead Hunters, down the hall...
The room has been unlocked. Now you must get to the map room and stop the Demon finding the contol centre. As you exit the security facility, you will hear a lot of screams and a loud explosion out side...odd. You scour the area, and find a lot of blood and a rocket launcher... but no human body...
Snipe the human survivors from the ledge using a Rod Rifle (the experimental predecessor to the Halo 2 Carbine), which can be found near the overshields. The survivors will be armed with pistols and most likely will be completely unaware of your presence-- the Grunts across form you on the ledge won't be so lucky however. Slide down the hill and hijack the flipped Warthog next to the wreckage of the dropship, then head back along the beach. You will be met with a scene of total destruction. Two ruined Ghosts. One crashed Banshee (PMI'd from Keyes). Blood and sand, piled high with human and Covenant corpses. There will even be the remains of a Warthog, torn apart by plasma grenades stuck near the engine. Continue on to the map room, where you will find only one surviving defender, a Hunter. He will remain outside and cover you while you proceed down, down, down...
Next, turn right to see the Shafted cutscene. You will be tackled by a petrified Grunt, who frantically tells you about the untold horrors that lie below. You brush him aside and reprimand him for his cowardice, jsut as a blood-curdling scream (Elite) echoes across the shaft. The Grunt just about wets itself and starts hopping up and don on the spot gibbering like an idiot (no need for any change then). An Elite will walk out to the platform and hand you his Rod Rifle. Using its 2.5x scope you zoom in across the shaft to see an Elite-sized shape, that just runs out, turns, and disappears into the shadow. You suspect that perhaps the Demon has a sniper rifle and is in fact a diversion, while the Marines search for the map, but consider it odd to use the Demon for such a menial task. You proceed through the facility, killing Marines as you encounter them, until you get to the map room and find the few Elite guards are dead. Damn, they made it...
Now your objective is to return to the surface. Simple enough, most of the Marines have already left, now only the rear guard (

) to contend with. Once you reach the dropship it will take you on the short journey to the small island outpost a few klicks away, where you are mystified to find the entire, 200-strong garrison deserted, and the walls stained with the blood of your brothers... Grab the connecting flight out before you discover what happened through first hand experience.
^Crazyness... Hard as hell to do though
As some of you may see the storyline is partly different from the original EC:SC.