Right off the bat, I must say I'm really digging Shadow Complex.  The side-scrolling shooter genre hasn't had a decent entry in quite awhile and I think it is due for a rebirth.  It's only fitting that this game comes from Epic, whose Gears of War franchise always seemed to me like Blackthorne in 3D.  I've only played for about 2 hours so far, but here's what I think.
 
First off the graphics are pretty fantastic, with lots of detail and great lighting.  The only knock against it is when the camera goes in close to characters for cut-scenes, but this is hardly worth slagging on.  I thought that the whole game would take place in this secret base, but there seems to be a good amount of variety of indoor and outdoor locations.
 
The controls work well though at the very start I thought the aiming was too touchy.  However, as I started to level up my aiming and accuracy stats it became much easier to pull off headshots.  There are a bunch of fun methods to take guys down including a devastating melee attack that sends ragdolls flying about.  The guns and grenades are also quite satisfying.
 
The exploration element of Shadow Complex is also pretty satisfying.  Your map shows you there's stuff in a given room and you're tasked to find out how to get at it.  This relieves you of endless backtracking and missed opportunities. I experienced a few clever puzzles required to get the power-ups (HINT: it's not always about using your flashlight to find the secret). 
 
There are a few complaints.  The story isn't very engaging so far, it's comprehensible to be sure, just not that great.  It kind of makes me wonder why they bothered using Orson Scott Card's name, when there really isn't anything, so far, that I haven't seen a hundred times before.  I kind of wished the games pacing was a little slower, everything moves really quickly, so strategy often becomes secondary to just blasting the hell out of everyone.  It all just seems a little hyperactive and makes me feel like I am rushing through it.
 
Thus far, a great game and more than worth the price.  Can't wait to keep playing.