Some early screenshots like this one betray a scope that dwarfs what Halo eventually became. However, an obvious design tradeoff is how much time can be spent on any one area of a gameworld that is so large without repeating. Here, while individual elements like the trees, rocks and bridges are detailed, they seem almost randomly placed.
Early shots and vids show the Master Chief running with his assault rifle resting on top of his right shoulder; this posture was eliminated from the shipped game for the Xbox. Here it looks like he's taken it down off his shoulder in preparation to fire on the Elite in the tunnel to his left.
Another weapon that didn't make the cut, like many featured in the Evolution of Halo video. The gatling machine gun also showed up in several early screenshots. The look of it, especially the rust on the heat shield, resembles the model of the flamethrower that was also cut from the Xbox version and resurrected for the PC and Macintosh versions of Halo 1.
Some of the early shots showed amounts of shell casings that were evocative of action scenes in The Matrix. One point stressed in early PR for the game was the phrase "persistent world". Some forumgoers wondered if that meant if every one of those shell casings would remain in the game world as an object, similar to the detritus from melee combat in Myth.
The human vehicles probably changed the most between these shots and the shipping game. This is most probably the Stealth Tank, which was very wide and low; as you see here, the crouching marine barely fits under the muzzle of the tank's cannon. The Stealth Tank did not make it into the shipping version of Halo 1.
An early Master Chief model fires on approaching Elites in a tunnel environment that looks like it's from the MacWorld 1999 announcement trailer. The game at this time had no AI; all events were scripted.
Each of Bungie's early screenshots featured a vehicle. Here, we see not just the Warthog that appeared in the first shot, but also two Banshees that appear to be very close to the final design. However, the grass textures are quite different, somewhat reminiscent of Halo's heritage in Bungie's Myth series. The background, as well as the look of the rocket launcher, are also quite different from the Halo we know today.
The first known screenshot of Halo. The Warthog, while recognizable, is still quite different from the final version. This original version of the Master Chief is completely different from what shipped in the game, and the scenery is also very different. Like many shots around this time, the spartan (no pun intended) but beautiful surroundings led some to speculate that Halo's entire territory might be traversable with vehicles, with terrain automatically generated by an algorithm, and designers adding detail to special areas.
This screenshot caused massive consternation for awhile on several Halo forums due to a reflection on the visor which resembled a skull.
This shot of a Covenant Elite shows a form very similar to what appeared in the shipping game. Earlier shots had models that were much more grey than purple, and more closely resembled slightly less muscular versions of the Skaarj fighters from Epic's game, Unreal.
The hat of the marine on the right here earned him the name "Fishin' Bob".