It is quite stunning. The playback, any canned stuff, happen in the game-world, and are woven seamlessly into it to an extraordinary degree. The world you inhabit changes, talks to you, you discover more of it, and from these things story emerges. Very complicated, very elegant. As a designer, I plan to play the game and chart out every single thing they did.
Trespasser pushes the envelope in other ways.
Whereas in its purely interactive elements a Quake level would be mapped as a set of walls, beasties, and traps, Trespasser is much more complex. I don't think people would disagree that it advances the state of the art in 3D reality. It lets you do more things you should be able to do in that reality, and it gives you new, interesting ways to hack around in 3space. Its story elements are built so as not to introduce non-interactive, or inappropriately interactive elements into the story. The other story, which is the story of nearly every computer game ever made, is one of increases in skill, triumph, and ultimately mastery over the virtual realm.