EDIT IN PROGRESS. ALL PICTURES MAY NOT BE UP AND GUIDE INCOMPLETE

Excavation Site: Affinity

Hit the spoiler buttons to read my ramblings/notes.

ES: Affinity is my first attempt at a map on Reach. Contrary to most people's impression of a "first attempt", I put alot of effort into this. I have well over 15 hours logged in the forging process and 3-4 in gametype tweaking. On a H3 map this wouldn't be that much, considering most of my H3 maps took me weeks to make. But, the new forging system makes things so precise, that I feel as if the amount of time I put into this map is the equivalent.

Before I go into the story of the map, I'd just like to point out that the money limit was reached, as well as the item limit in multiple sections. I had to cut back alot. I had planned on building a city, but had to settle with an outpost. In the end though, I truly think that I captured what Bungie tried to do with Invasion, but in my opinion, failed.

As a Spartan.

Crash landing on the beach front, you are disorientated. You were shot down, but you don't know what from. You look out the windows of your ship and see a Covenant strong hold. AA guns are on the rock wall to your left. They must've been what shot you down.
We need to get through that wall and disable them. It's our only hope.

It's time for an Unplanned Invasion.

Phase 1:

Loadouts:
Drop Shield + Grenade Launcher + Magnum
Hologram + DMR

Elites:
Evade + Plasma Repeater
Armor Lock + Plasma Rifle

My reasons for picking these as your initial loadouts are simple, and tie into "my" version of what Invasion should be(As explained at the end of this post).
It is impossible to reach the first objective without Drop Shields. Period. They also provide cover for you and your teammates, since the only cover is fallen pieces of your ship. The Grenade Launchers are also good for clearing out the bunkers on the bottom. middle. top. and side of the Covenant wall. They can also disable the Shade Turret in the Trenches.
The DMR choice is simple. Holograms are awesome and DMRs are the best way for taking out enemies on the walls.

Elites:
The Elites loadouts were chosen to make them seem slightly underpowered

The Armor Lock class is for those who want to spawn in the Trenches, at the front lines. They were only given a Plasma Rifle so that they are not extremely good in CQC. The Evade class was chosen to give those who like to play tactically some fun. Being a one shot and barrel rolling behind cover is pretty much the definition of awesome. Right alongside hologram, of course.

The main objective of the Spartans is to plant a bomb at the base of the wall. Obviously, it is going to be a challenge. The only IED that survived the crash landed at the base of a nearby rock. It just so happens that this IED is old. Very old and very heavy. You will have 50% movement speed while carrying it.
This isn't your only obstacle, however. The entire top of the Covenant wall has plenty of bunkers for the Elites to rain hell upon you. They can also get to you from the Plasma Turret mounted in the middle-rightside of the wall. Not only that, but they seem to have trenches located on the right side of the beach, with a Shade Turret at its forefront.
If the plant is successful, it will almost instantaneously combust.
Overview:

Crashed Ship:

Trenches:

Objective:

The wall will then blow up and a new entrance will open up.

Begin Phase 2.
With a small hole blown into the wall, the Elites in the trenches are forced to retreat. The main control room opens the door behind them for quick-access back in. Surely this door will help us with our invasion.

Loadouts:
Hologram + Shotgun.
Drop Shield + DMR.
Evade + AR + Magnum.

Elites:
Hologram + Plasma Repeater
Evade + Needle Rifle + Plasma Rifle
Armor Lock + Spiker

Again, the choices were chosen while taking multiple things into account.
The Hologram + Shotgun combo was chosen so that the small hallways and short corners could be controlled. However, a secondary was taken away so they would only be good at one thing(Again tying into my idea of Invasion(Explained at end).
The Drop Shield + DMR was chosen because it is still possible for the Elites to push the Spartans back to the beach. In fact, it is their main priority. They must balance clearing their base and pushing back the Spartans at the same time. The Drop Shields are there to keep cover and the DMRs for clearing the roof. However, they are still very useful in the long hallways and the control room.
Evade + AR + Magnum was chosen for those who want a balance. They specialize in medium and close range. With the AR good for taking out shields, while the magnum gets the final shot in. Evade is also good for quick beatdowns and getaways.

Elites:
Hologram was chosen for those who like to be overly defensive. They have the strongest of the Plasma rifles, and are good at tricking the enemy into thinking they are safe to chase after an expecting Elite. The Evade class was chosen for those who want to be a combination of the defensive and offensive. They have a weaker close range weapon, but are the best at defending the beach from the wall. The Armor Lock class was chosen so that noobs have a chance.
Just kidding. They are actually the best at medium range. The spiker is an extremely good but underrated weapon. Combine it with invincibility and you have a great combination.

Entering the Covenant Stronghold, you spot the control room. Hacking one of the terminals there should disarm the AA guns and we can use our last falcon as an escape. But it seems to be close to an Elite-Spawn-Hive. This could prove tricky. Perhaps we should go straight for the AA Guns themselves. They are further off from these hives but we must scale the multi-tiered stronghold to access it. Whatever our choice, we must not fail.

Control Room:

Terminal:

AA Guns:

With the AA guns disabled the Spartans can now travel home...or CAN THEY? One Spartan reported seeing a Covenant Outpost in the outskirts of this landmass, and worse yet, he reported seeing dig equipment. Could the Elites have found another artifact...We can't risk this. We must get it to Halsley at all costs.

Begin Phase 3.

After disabling the AA guns, the remaining Elites took down the back-door-shield-doors and scurried off to the excavation site. We have taken up occupancy in their stronghold, and have brought in some weaponry that was scattered among the remains of our ship. The Covenant Outpost has also seemed to be fortified. Medium Class vehicles have been spotted, as well as a Banshee. Little do they know that with the AA Guns disabled, our Falcon can now lift off and our jetpacks can be put to use.

Loadouts:
Sprint + DMR
Jetpack + AR + Magnum
Drop Shield + Grenade Launcher
Invis + Shotgun

Elites:
Jetpack + Plasma Repeater
Sprint + Needle Rifle
Hologram + Sword
Drop Shield + Plasma Rifle
Invis + Spiker

It's getting late. I'll do this tomorrow.

Phase 3 is the most interesting of the phases. It is wide open and 10 minutes long. The elites are given long respawn, long range weapons. However, the Spartans have access to a Falcon quicker than the Elites do to a Banshee. As long as the Falcon pilot avoids Plasma Pistol shots, you should be good.
Oh, the objective. So you must bring the artifact out of the dig site and to your ship. This is a very long run. You move at 50% speed, have 90% shields and no health regen(shields are normal) it is also too large for a Spartan to bring into the passenger seat of a vehicle. The core cannot be returned by the enemy as it is considered too holy for the lowly Elites to touch. Wherever it is dropped, it is defended. Once the artifact makes its way to the now controlled Spartan stronghold, the Elites can only do short bursts of defense and unless there is a short amount of time left, they're screwed.

Elites have access to a Ghost and a Revenant, as well as a Banshee to counter the Falcon.

In all honesty, this part will seem like it is boring and goes against the whole idea of the rest of the map. But once its played, you'll realize its just complimenting the rest of the map.

Excavation Site:

Falcon:

With the artifact secured we can return home.

My take on Invasion.

This map really displays what I think Bungie tried to make Invasion.
I believe that Bungie intended it on being a gametype where no one person can make the team win. You need your temmates by your side. Each class not only fills a player's gameplay niche, but one that is necessary for progression. However, I feel as if I'm simply playing Bad Company with a Halo twist. Don't get me wrong, BC2 is one of my favorite games of all times, but it doesn't work in Halo.

With my map, I feel as if I captured what they intended. Take Phase 1 as an example. Without DMR classes the walls and bunkers will be overrun with Elites raining down hell. But without the Grenade Launcher, the Shade Turret would destroy the Spartans and there we be virtually no cover for them.
In Phase 2 not every elite can pick a needle rifle because the map is no longer far range confrontations. The Spartans can also just not all pick a shotgun because the needles would overwhelm them.
Phase 3, however, is really where I think Invasion was meant to be. Long range, extreme teamwork, and lengthy fights. For starters, the Falcon is necessary for taking out pesky elites hiding in the background. They are also useful for picking up Spartans being overwhelm by Elites. But without unites on the assault, the plasma pistol would easily knock the Falcon out of the sky. With the flag carrier, he can't get more than 10ft without being covered on all sides, and without Drop Shields being placed along his path. He needs to rely on his teammates and his teammates need to know they can rely on him.