I picked up Advent Rising for the Xbox a few days ago.  It got a fair review, with the bad part of the review coming from the game's poor targetting mechanics.

In it, the human race, having just survived a civil war of some kind, is about to make first contact with the Aurellians, an alien race far more evolved than our own.  Still, however, the Aurellians (as well as many other aliens) hold the human race in very high regard, almost as gods.  Unfortunately, another alien race, known only as the Seekers, found out about the meeting and that the humans are in existence -- and they come to destroy the human race.  When you first meet the Aurellians, you're on a space station over some planet (not Earth), and they mention something in passing about the destruction of the first human race, which indicates that there is no Earth, and that we'd already been vanquished once.

In general, the game plays as a 3rd-person RPG, although I read in the instruction manual that you can switch into first-person mode without certain abilities.

The biggest problem in the game is the "Flick Targetting" system implemented in 3rd-person mode.  While it's a novel idea and a fresh approach to 3rd-person shooter mechanics, it falls flat on its face, and brings the game with it.  Essentially, you use the right analog stick to pan and tilt the camera, but you also "flick" it in the direction of an enemy to target it.  At least, it's supposed to work that way.  There isn't any convenient way to un-target something, and it seems that you auto-target an enemy shooting at you if you're so much as touching the right analog stick.  Another of the mechanics problems is that it seems enemies come at you forever -- which is fine, and actually helps promote the feeling that you're in a war where aliens are invading (that's what's happening), but a LOT of gamers who have played fighting games expect that you don't leave an area until you've laid vanquish to all your foes.  That simply doesn't seem to happen here -- I can stay in an area for 10 minutes and wave after wave just keep coming.  It's hard then to know when to move on, or if you should even bother with the bad guys at all.

Those were the two problem areas I've found.  I haven't quite gotten to the point where I get supernatural powers though, so there may be some there.

On the positive side, the visuals are absolutely amazing.  The water effects could use some work (it is either too opaque or too transparent when it's there), but all in all, it's a work of art.  It's also nice that, instead of a boring loading screen, they provide cinematics during load times.  This was a welcome departure from Halo's loading-between-every-level style (that wasn't in Halo 2, so don't get me wrong -- but even the first time you load the game, it takes you back to the cinematic before your last checkpoint).

The soundtrack is absolutely phenomenal.  One of the very best, if not THE best, of any video game soundtrack I've ever heard.

It's definitely worth getting.  It's a planned trilogy, and I'd imagine that before the next game, the polish will make the title truly shine.