According to Blend Games, Borderlands not only has..."more guns than Halo 3, but it also has more weapons than Call of Duty 4: Modern Warfare, BioShock and Turok, combined. That's a heck of a lot of firepower at a player's disposal."
The article continues on to say that they will "drop the details on how so many weapons have been made accessible, and what some of them can do."
