The process we went through to balance the difficulty is pretty rigorous. Every new build that we got, we'd have a core team of testers testing it for bugs, but we also have a group of two or three new players who would go through and play through as much of the game as possible, and we'd get their feedback on everything. A lot of the difficulty tweaking was done on a level-by-level basis. Some of the time limits were too strict or the enemy A.I. was too aggressive.