I just picked up Uru: Ages Beyond Myst, and it's incredible.
1. The game is huge. I mean really really huge. Picture Metroid Prime. Twice. That's pretty close.
2. It's full 3D, and it looks GORGEOUS.



3. The level of customability is insane. You write in your own journal to document things, use the KI (pronounced Key) to take pictures of your surroundings for later reference, etc. But on top of that, you can completely customize your character, down to the wrinkles. Everything's color can be adjusted minutely, as can physical attributes (such as weight, eyebrow size, etc). You can also customize your "home" of Relto.
4. Online play. Nuff said. The game can be played on single-player, but what's more fun than exploring hugeass areas with other people AND having built-in voice chat?
5. Every bit of sound is incredible.
My highest recommendations, you must check it out.