Halo 2 E3 demo

Halo 2 E3 Demo eG2m4_XVLDM The Halo 2 E3 Demo was a real-time demonstration of early plans for Halo 2's Outskirts and Metropolis levels.

It was shown at E3 2003, and showed some designs for Halo 2, including ODST's, Battle Rifles, (which were originally going to be single-shot), Dual-Wielding, SMG's, Brutes, the Gauss Warthog, and many other things.

Differences with the final game
The demo had a vastly different storyline from the final game. Much of it was essentially rewritten to change the events.
 * The New Mombasa Orbital Elevator is nowhere to be seen. Instead, a massive building complex dominates New Mombasa's skies.
 * The Pelican Master Chief lands in is not destroyed, instead it lands normally and disperses its troops without a problem.
 * The crosshair is in the Halo 1 position, in the center of the screen, there is also a much larger field of view.
 * Master Chief passes through a battlefield hospital before engaging Covenant ground troops in combat.
 * Sergeant Banks is an injured marine who gives Master Chief his SMG, introducing the Dual Wielding feature. He is directing an attack against a Covenant artillery cannon, instead of a Scarab.
 * Brutes attack Earth side by side with the Elites.
 * The Chief is trying to destroy one of many landed CCS-class Covenant battle cruisers, instead of a single Assault Carrier.
 * The Battle Rifle reloads like an Assault Rifle.
 * In the Pelican there aren't normal Marines, there are ODST's inside it.
 * The Master Chief fires the SMG's at the same time, and he never reloads them.
 * When the Master Chief changes to the Battle Rifle from the SMG's, he doesn't drop the other SMG.
 * The battle rifle is semi-auto and has no ammo counter
 * The Shadow's turret shoots green plasma blasts that look like charged plasma pistol shots, not purple shots. Also, it shoots more automatic, it doesn't get faster as it shoots.
 * It is Cortana, not Lord Hood, who outlines the mission (defeat Covenant ground forces and destroy their cruiser, instead of infiltrating their carrier to capture the Prophet of Regret).
 * Only one Pelican, instead of three, heads to New Mombasa. Also the In Amber Clad is not seen.
 * Major Easley does not appear in the final game.
 * The Elites you see are either some sort of stealth elites or some sort of new elite that didn't make the game.
 * The Brute Shot shoots some sort of plasma grenade which flies straight instead of the frag grenade that falls and bounces after a few feet.
 * The Plasma Pistol shoots a larger bolt.
 * Grunts were seen driving the Shadows, as well as Ghosts.
 * The Phantoms have a different appearance and are destructible.
 * The Grunts and Jackals died the same way they did in Halo 1, with an ocean of blood that fly's out.
 * The Fragmentation Grenades made the same type of explosion like they did in Halo 1, but are much weaker.
 * When a brute jumped on top of Master Chief's warthog, he knocked out two marines instead of just one.
 * The Brutes are weaker than they are in the final game and were easily killed.
 * The Battle Rifle's melee attack shows three different animations at the same time instead of only one at a time--this was the first animation shown by Bungie of their proposed "melee combo" system, which was cut out of the final game due to time constraints.
 * Pete Stacker may have appeared driving a Gauss Warthog like in the final game but is killed by a Brute.
 * When the Chief shoots a Phantom with a Gauss Cannon a green and blue plasma spark appears.
 * The Gauss Cannon has a faster rate of fire.
 * The Prophet of Regret does not lead the Covenant invasion force on Earth.

Other Links
It can be viewed here: http://files.mythica.org/halo/halo2_e3_realtimedemo_hires.mov Or downloaded here: http://www.bungie.net/Games/Halo2/page.aspx?section=AudioVideo&subsection=GameVideos&page=1