Halo: Reach is the first game in the series to add sprint. As a speedrun, it has many tricks, but it is less popular than the main trilogy.
Halo Runs record page: http://www.haloruns.com/records?lb=500 (click the timestamps for video links)
Sprint and jumping
Unlike other games with sprint such as Call of Duty, in Reach your sprint meter continues to be used up if you jump while sprinting. This means that bunny-hopping is not useful as a sprint preservation technique. However, since jumping preserves some of your momentum, you can gain a little extra distance out of your sprint by jumping at near the end of a sprint. Testing shows this can save over a second for every 4 full sprints. http://pastebin.com/V5VruCH6
- Winter Contingency
- ONI: Sword Base
- Tip of the Spear
- Long Night of Solace
- New Alexandria
- The Package
- The Pillar of Autumn (Halo: Reach)
- Lone Wolf
The enemies in Reach underwent a major change from the main trilogy. Elite ranks were reorganized. In addition, AI of other enemies behaves somewhat differently.
Major Elites in Reach are a red-orange color, not to be confused with the gold armor of Generals. When unshielded, they can sometimes withstand a melee.
White Elites (Ultras) in Reach are quite common, much more so than in Halo 2. They will occasionally use Armor Lock to tank explosions, such as grenades or needler supercombines. Unlike in Halo 2, they possess no sword pull ability, they will run and charge at you like any other Elite.
Gold Elites (Generals) in Reach have the strongest shields of any Elite, even stronger than Zealots. They are also fairly common. They are usually found wielding swords or heavy weapons (FRG/Plasma Launcher).
In Halo: Reach, Jetpack Elites (Rangers) were changed so they can no longer continuously fly. Instead, they perform extended jumps, much like Jump Pack Brutes. They have been seen using plasma repeaters, needle rifles, concussion rifles, and focus rifles.
The Invisible Elites in Reach are a cross between the Spec Ops and Stealth Elites in earlier games. They have a Spec Ops range of weaponry and the Stealth Elite's weaker shields and constant active camo.
In Reach, Zealots are changed to be a maroon/purple color. They appear on the levels Winter Contingency, Tip of the Spear, and The Pillar of Autumn (Halo: Reach). An extra-strong Zealot, the Field Marshal, is encountered on The Pillar of Autumn. He's noticeably faster and more responsive, and carries two weapons, fuel rod gun and energy sword respectively.
In Halo: Reach, killing one Brute after another often triggers a chain reaction of berserking. Imagine the Brutes as operating in pairs, like the Hunters in Halo 2 and 3. Berserking Brutes will rush you in an unconvincing manner, compared to the fast moving ones in Halo 2 and 3.