Valve co-founder Gabe Newell is credited in the game as an additional tester. More information on his involvement can be found in an extensive write-up by director and producer Warren Spector published by Gamasutra a few months after the game's release in 2000. Newell was the first of several industry friends (including developers from Looking Glass Studios and Irrational Games after him) to play-test and criticize the prototype missions they had ready in mid-1999, with Spector noting he "correctly identified the utter lack of tension" in the game's skill and augmentation systems, forcing them to completely change their design approach, with lead designer Harvey Smith revising them significantly for the final game.