Metroid Prime

It just looks incredible. The screens I have seen, and previews I have read make it feel like playing through a strange mix of Aliens and Indiana Jones.

When Samus goes into Ball Form, the camera goes into third person mode. I think it does the same thing for her Super Dash and Grappling Beam. Also, the interface of the game is made to feel like you're actually in her Power Suit. So, you can scan a certain enemy and bring up statistical information and biological data on any creature in the game. I was viewing a teaser video for it a few weeks ago, and watched a scene where Samus obliterates a corridor full of nasty spider-like aliens, and has to wipe the blood and guts off of her visor.

One of the other really cool additions to the game is Samus' Infra-Red Scanner. I've seen a few screens, and it looks just like Predator.

On top of all of this, the bosses are massive, the enemies come in swarms, and it just has a much more innovative and professsional presentation than really any other first person game out there.