The best game intro I've ever experienced is Homeworld. It's also worth a look because the way it blends the hand-drawn visual style in the first section with the 3D elements later reminds me somewhat of the visual style we've glimpsed in the Elemental engine. http://www.youtube.com/watch?v=yrW4jkQdmjI
Another favorite of mine is the Freespace 2 intro, although it's a pale second to Homeworld. http://www.youtube.com/watch?v=khIWdolT9xY
The things these two share that make them work for me are a sense of the history and setting of the world I'm about to enter, fantastic and appropriate music, and killer voiceovers. The sense of melancholy they share would also fit well into an Elemental intro.
Also worth an honorable mention is Myst. Can't say I really loved the game, but it was a great intro. Not sure how applicable it would be to Elemental, though.