The final confrontation with Dr. Breen in Dark Energy is designed as both a spectacle and a moment of reflection, leveraging pacing, music, and visual storytelling to deliver a memorable ending.

Breen and the Combine's architecture were more sinister and overbearing as well. The demo shows off early versions of major NPCs like Barney and Alyx, as well as an almost-unrecognizable Dr. Kleiner.