The opening level of the game was originally envisioned to have a much larger zero-g training facility complete with warthogs and other vehicles. The purpose of this was going to serve as a way for the Chief to transport the giant bomb the Covenant left on board. Instead the level got cut back and transporting the bomb was kept to a cut-scene.
The largest trailer for this game was released in movie theaters. Near the end of this trailer, the usual www.xbox.com URL is replaced with "www.ilovebees.com" for a moment. If someone goes to the website, they encountered a website which seemed to be under the control of a Halo-type artificial intelligence. This website continued to change, eventually telling a multifaceted story which explains how the Covenant find Earth in Halo 2, despite not knowing its location during the events of Halo 1.
In the series "Red Vs. Blue", a glitch in the first Halo (2001) that made characters looking down appear to be looking forward was the only reason that Red Vs. Blue could be made. In Halo 2 this glitch was fixed. Instead, all you have to do is spend all of your grenades, and then press and hold the grenade button. This drops the character's arms. Correction: Grenades did not have to be spent. Simply pressing down on the Xbox controller 'Directional-pad' lowered the character's weapon.
The second level of the game was originally going to be on board a Covenant ship the Master Chief boarded after leaving Cairo Station. You would have to fight your way through the ship and destroy it from the outside. This would have been Miranda Keys's breakout level as she would have assisted you. The level was cut and a bomb was added so the Chief could blow up the ship in a non-interactive cut-scene.
Although the game was critically acclaimed, the developers felt that it could have been better. In a 2007 interview with Edge magazine, it is noted that they didn't have time for their customary "polishing" phase of development. A commentary for the game, featured in the Halo 3 (2007) "Legendary Edition", elaborates on this, describing sections of the game which had to be dropped in order to meet their deadline. The game would have continued past the much-maligned "finishing this fight" cliffhanger, to a final level on the Forerunner space ship.
The only enemies encountered whilst playing as the Arbiter are the Heretic Covenant, the Flood and the Covenant Loyalists (Brutes, Jackals and Drones). No hostile Humans are ever encountered during the game.
Microsoft predicted that the first day sales would amount to almost US$100 million, a staggering figure for a video game. In fact first day takings managed to surpass even that estimate, reaching the US$125 million mark after only 24 hours of sales. This means that this game earned more on its first day than any previous entertainment media release - including every major Hollywood blockbuster (the biggest opening day earning for a film at the time was Spider-Man 2 (2004), which took $40.5 million when it opened in June 2004). A Microsoft representative was quoted as saying, "The first 24 hours of Halo 2 sales have taken our breath away."
When the game was initially released on PC, modders found game files with the extension .ass. Sometimes when they tried to modify it an error message popped up with a picture of someone's butt on the right. Some developers at Bungie found the extension .ass to be humorous and that they had to put an actual butt in the game files. This caused Microsoft to delay the game and add an additional rating descriptor for Partial Nudity.
There are two versions of the game, the normal version in the standard green XBox DVD case, and the Limited Collector's Edition, sold in a metal case with a bonus DVD that includes "Making of" featurettes and extra content. The manual for the Collector's Edition is also different from the normal version; where the normal version shows everything from the point of view of the human forces, is orange in color, and has the Master Chief on the front, the CE manual is purple, shows everything from the point of view of the Covenant, and has an Elite with an energy sword on the front. Also included in the CE was a small booklet titled "Conversations from the Universe", a collection of one-page stories between major and minor characters that provides some additional background on the universe of Halo.
The trivia item below may give away important plot points.
A level which would've taken place after the death of the Prophet of Regret involved the Master Chief finding an ancient Forerunner tank and using it to explore underwater eventually discovering the Gravemind. The Gravemind would have been front and center for this level, with tentacles sneaking away from behind doors only hinting to his existence. However, this level was cut because of time constraints.