Delusions

"A trip into virtual reality: all begins with debugging a VR system, but then things get out of hand. Who is Morrodox, what has he to do with your colleagues, and what is going on?"

You're working in a Virtual Reality lab, helping to debug the next generation of sim technology, until a suave stranger forces you to confront the creeping air of inconsistency that's been in the corner of your consciousness. A dark one, with surprises up to the end, one of the coolest villains I've seen in a long time, and some quite impressive feats of Inform programming. The structure is unusual, with a nightmarishly looping midgame that resembles its frame in form but not in content.