Introduction: Halo's first level is a relatively simple introduction to the game. You are introduced to the Covenant, mankind's alien nemesis, and they are introduced to the heel of your boot. Your orders: Survive to get off the Pillar of Autumn and bring the shipboard AI, Cortana, with you. If you fail, the Covenant will obtain her navigational databases and may find the location of Earth. Failure is not an option.

Part 1: Pillar of Autumn
Admire the game's opening cutscene again. (I can never get enough of looking at the Pillar of Autumn.) Listen for Sergeant Johnson's speech to the Marines-- it changes with each difficulty setting, and this one is quite humorous.

Wake up from Cryosleep and head for the bridge. Don't follow your Navy tech friend too closely: He won't last long. There's only one way to the bridge-- not too complicated. Watch out for the grenades exploding (they still hurt, even though they are scripted), and keep moving. Once you reach the bridge, a cutscene will begin.

Cutscene. After the loss of the ship's main cannon, Keyes initiates the Cole Protocol, assigning Cortana to the Master Chief's MJOLNIR battlesuit for safekeeping. His orders are to find a lifeboat and exit the ship, evading and destroying the Covenant on the way out. He will then land on the mysterious ring-planet artifact below to link up with the Marines.

Part 2: A.I. Constructs and Cyborgs First
Captain Keyes wants you to get your butt off his ship. Don't worry, it's nothing personal.  Once the cutscene ends, you will be armed with a trusty M6D pistol. Three Grunty friends await you in the doorway. "Where did they come from?" Guess the situation is worse than anticipated.

Proceed into the mess hall and the first real battle on Legendary. The MA5B Assault Rifle awaits you in the doorway. Two Elites and a Grunt are standing on the other side of the room. Take out the Grunt with your pistol before he notices you and starts shooting. This accomplishes a twofold purpose. First, the door behind the Elites will open, allowing several Marines to enter and engage the Elites. Second, Grunts tend to draw their Elite commanders' attention to you. This will minimize the risk of being fired on before you're in range of the assault rifle.

The Marines will pour fire into the Elites as soon as the door opens. They won't last long unaided, so take the opportunity to whack the Elites in the back. I recommend swapping the AR for a Covenant plasma rifle. It is extremely effective against Elites in the close quarters of the ship's corridors, when they have no room to dodge.

Note: After the cutscene with Keyes, if you can get off the bridge before the objective "Get off the Pillar of Autumn" disappears from your screen, you will be rewarded with the ability to carry a third weapon. This will make the next engagement slightly harder, however. Pick up the AR in the doorway, add a plasma rifle once you have killed the Elites, then go back to the bridge and get the pistol. Three weapons. (This trick is significantly easier if you have the controller sensitivity cranked up.) 

Once the Elites are dead, hordes of Covenant will pour forth from another hallway. Find the hallway they came in by, eliminating the Elite that stands in your path, and kill the Grunt stragglers that hold the hall. From here, you are free to move on and ignore the massive freaking threat to the bridge and the Captain, but I prefer to play a little game with the Covies. I call it "Peek-a-boo, I see red". Take out the enemies closer to the hallway entrance one by one, ducking back into the entrance to recharge shields, then move out, exposing yourself for a short period of time every few seconds to kill enemies that present themselves. Grunts are easy targets, so take out as many as you can without draining your shields. There should only be two Elites left, so deal with them individually. Stock up on ammo and grenades after everyone is dead. Grab the health and move on. A lone Elite challenges three Marines. Use body language to demonstrate the beautiful texturing of plasma rifles.

Around the corner is an airlock, which a boarding party of Covenant are trying to enter through. Block their path with a plasma grenade, then toss another one farther into the boarding pod. Make sure and mop up any stragglers before taking an overshield from the back of the pod. Continuing on, a split in the hallway. One way leads to a battle between several Marines and four Elites. Go the other way. By doing this, you will flank the Covies, and you will then be free to take them out from behind with grenades. Be wary; the ones you don't kill with the first couple grenades will come after you. Moving on, there is a similar situation; simply go straight and flank the Covenant; only two Elites this time.

A second group of Covenant on a boarding craft have decided to join the party. Don't they ever learn? (Yes, because you are the Master Teacher of Hard Lessons.) Teach them the Ultimate Hard Lesson (not to mess with you), but get there before the Marines do. The first Elite of three comes around the corner with a few Grunty subordinates. Stick a grenade to a Grunt and be amused at his plight. If he doesn't take the Elite with him, use a second grenade. That leaves two Elites in the hallway. Take out your Plasma Rifle if it isn't already, then come around the corner swinging. Then run and hide before they take out your shields. Repeat as necessary. Grab an overshield and move on. Another flanking box is ahead, but this time go straight for them. Look to the right as Covies pour out of the door. Chuck a grenade between the door and the thing in front of it, and watch the first Elite fly. The second sits in the other hallway, the one you could have chosen at the split. After taking him out, go back for the second overshield, which you should need by now. If you don't, swap your Plasma Rifle for an AR and fire into the ovoid stationary shield, which will bounce your bullets back at you and take out the remainder of the overshield.

All that because you will really need a full overshield for the next encounter. Swap your M6D for a plasma pistol, if you haven't already, but remember where you put it. Cortana will tell you there are "Covenant, on the landing above us". That's your cue to get your butt up those stairs ASAP. Charge up the plas pistol, unload it into the elite that will probably show himself on the way up, and follow up with a few more shots from the rifle. If you miss, don't go back or you will start taking fire from above. Go to the area left of the stairs. When the door begins to open, toss a couple grenades through the crack, which will hopefully take out a few Elites. "Tresspassers will be shot. Survivors will be shot again." Take cover and eliminate the survivors, watching your shield strength. Grab fresh weapons, recharge your shields, and head into the hall next to the landing. Take a left and throw a few grenades, then duck. Finish off the stragglers with a steady stream of plasma. Proceed around the corner with caution, taking out the Grunts quickly, then hose down the Elites waiting up ahead while making them dance with plas grenades. Go on and get the health by the window, then go back and get your pistol if you want to.

Around the corner are more Grunty companions just dying to be your pal. Show them they are unloved. Go into the maintenance shaft. As you make your way to the first exit, you will see a grunt just outside. I recommend a healthy dose of Sticky™ plasma pills. "NOT AGAIN!" screams the Grunt, hopefully to the Elite he will run up to. At this point, it is good to hear a double scream of pain. Back up, find the tunnel to the right, and head down it until you find a left turn. You will come upon the same group of Covenant you just avoided. Stick another Grunt. Go back into the tunnels, this time the way Cortana suggested in the tutorial. Go through the halls to find the group of Covenant, yet again. If either Grunt made it to his commander, both of them will be dead, leaving one less Elite to deal with here. You know the drill by now. Take 'em all out. An Elite will be waiting for you in the hall leading to the cryo-chamber, so be careful.

Run through the Cryosleep bay and kill the Elite at the end of the hall. By this point, I prefer to have the combo of both pistols, human and plasma. Overcharge the plasma, drop his shields, switch to human, and a headshot drops the Elite. More headshots will take out the Grunts around the corner. Through the maintenance shaft, more Covenant are engaged with some Marines. Help out your buddies with a grenade or two. Go into the hall and take out the chicken-hearted Grunts somewhere to your left. The last battle of the level awaits.

A huge rack of fragmentation grenades is just ahead. Note: Once I walked up to the rack fast enough that the message that appeared told me I had picked up 5 grenades. Yet I only had 4 in my inventory. Cheap @*!&$. Approach slowly. Pick up a bundle and throw indiscriminately. There's plenty more where they came from. When you stop hearing roars of pain, move out from behind the rack and proceed down the hall. One Bumblebee-class escape pod awaits. Hop in and head dirtside. "The Autumn! She's been hit!" (No crap, stupid Marine.) The Covies won't have Cortana today.