developer blog at the Platinum Games website, director Shinji Mikami discussed the changes Vanquish has undergone during development. In the beginning, said Mikami, Vanquish was "an open battlefield type of game, where the goal was to move around crushing enemy positions." As development progressed, however, it became clear that an open environment hurt the game. The reason, according to Mikami, was an increased level of "visual density." There were so many things happening on screen -- special effects, loads of enemies, etc. -- that it was hard for players to focus on the objective.
"In an environment where we were doing whatever we pleased," noted Mikami, "it became pretty obvious that there was no good way of keeping your eye on the prize – the enemies you are targeting." As such, a more linear style of play helps keep players focused. Furthermore, Mikami also notes that the staple enemy, a robot called a Gorgie, was changed from white to red in order to make it stand out from the predominantly gray background.
If Vanquish turns out to be anything like Platinum's most recent action-fest, Bayonetta, then helping players focus on killing baddies is probably a good decision.