Deus Ex - The Deleted Scenes @ Eurogamer

Eurogamer looks at how Deus Ex evolved during the development process:

Story wasn't the only reason for editing Deus Ex away from its original vision, however - fiscal and technological realities played a role too. Sheldon mentions a mid-game level in the White House level as a particularly complex task for the level designers to realise and the decision was ultimately made to focus that effort elsewhere. In a post-mortem lecture filmed in 2008, Warren Spector lays decisions like this at the feet of designer Harvey Smith.

"On a daily basis I was building the rooms," explains a humble Smith. "So, I knew how big a room could be before the renderer would choke and how many guys we could have on screen. I had an intimacy with the tools."

Armed with this technological understanding, Smith approached Spector and argued for what he considers the two most critical changes to the original vision. The first was a new skill system with fewer abilities but more demonstrable effects - so the guns didn't do more damage but instead got easier to use as you advanced. The second was a trimmed down version of the story that abandoned the Mexican invasion and space stations in order to become more technologically feasible and narratively intimate.