A similar report showed that in the game's first level, called Jungle, players often ran out of rounds for their rifles. This was a mystery, because the designers had been careful to leave more than enough ammunition lying around. The team checked Pagulayan's video records and found that people were firing at the aliens when they were too far away, misjudging the range of the weapon and wasting bullets.
At first the designers couldn't figure out how to fix this problem. But then Griesemer stumbled on an elegant hack: He made the targeting reticule turn red when enemies were in range, subtly communicating to players when their shots were likely to hit home. It worked.
The ideal in gameplay, the goal every developer aims for, is an experience that keeps players in a "flow" state — constantly surfing the edges of their abilities without bogging down. Modern videogames are often compared to Hollywood movies, but the comparison, many Bungie designers will tell you, is inaccurate. A movie is static. "You sit there and absorb it all in a single two-hour shot, and it's perfectly linear," says Frank O'Connor, one of the writers tasked with scripting the story line in Halo 3.
Creating a game, in contrast, is like a combination of architecture — constructing environments that influence the behavior of people inside them — and designing a new sport. Gamemakers have to devise a system of rules and equipment that gives players a few basic goals and then allows them to find their own ways of achieving those goals. The flow comes from constantly discovering innovative ways to solve these open-ended problems.
Of course, this means that players will sometimes surprise game designers by doing things even they never thought of. This spring, executive producer Jonty Barnes watched a tester run around in a multiplayer level of Halo 3 that's constructed like a deep canyon. A bunch of Gravity Lifts were scattered around the bottom, and the player was bouncing from one to another. Then the tester got a clever idea: He grabbed one lift and, holding it, jumped into another one, launching himself up onto a high ledge. He then placed the second lift on the ledge and used it to bounce up even higher, landing on the top rim of the canyon. That area wasn't even supposed to be accessible to players.
"So he's up running on the canyon ledge, and the engineers are going, 'Christ, how the hell did that happen? Do you know what kind of bugs this is going to cause?'" Barnes laughs, a hint of pride in his voice. "But that's what you get when you set people free in your world."
Halo 3 is a vibrant, beautiful game, but it's also a bit cartoony. It doesn't have the eye-popping verisimilitude of, say, Gears of War, a rival Xbox 360 hit from Epic Games that dazzled fans last winter. Many critics have made this same comparison, and it's a sore point among some Bungie designers. They like to note that Gears of War — like most of today's shooters — takes place mostly in narrow corridors with only a few enemies at a time, so its makers can lavish attention on every square foot of space. Halo 3 is set in sprawling outdoor levels, with dozens of alien enemies swarming onscreen at once. The vastness of the game's geography means that gamers can replay each battle several times, trying several radically different ways to fight through it. It also means that Bungie's designers have to spread the Xbox 360's processing power around more thinly.