One word: Incredible.
I've been playing this game for hours now, and I barely noticed the time passing. From the awe inspiring graphics to the thundering sound, from the tossing of super power weapons to the chattering of the machine guns, this is one of the best shooters I have played in forever.
If you have a Direct X 10 video card, the water and lighting effects look outstanding. Even with DX9, the graphics are still great. Water blurs your vision if you walk under it, smoke clouds the air, and frost obscures sight. The water reflects the environment, and sends shimmering reflections down the corridors.
The textures are all pretty sharp, and the mapping is superb. My one gripe is that you can't blow things completely apart. A game like this would have been great with destructible environments and deformable models. I'm guessing we missed out on those aspects due to the simultaneous programming of the Xbox 360 version.
The plot is pretty forced, but you honestly don't miss it much due to gasping over the rest of the game. The backstory is much more interesting than the plot, however, full of retro 50s social issues and trappings. Honestly, I could feel the similarities between this game and the System Shock series developed by the same people, and that is a good thing. It's almost like System Shock 2, but the RPG aspects are toned down and the combat sped up, which is perfect for shooter fans.
Speaking of shooting, you do get some nifty guns, but by far the most interesting thing to destroy your enemies with is the genetic mutations you are capable of getting. An electric bolt from your fingers can stun someone like you were a human stun-gun, but if that person happens to be standing in water, it will fry his brains. You can toss a fire ball from your hand and watch your enemies writhe in flames (or jump in to water and create a huge steam cloud when the flames are doused), or you can ignite the surrounding scenery and really watch the fiery carnage.
Finally, the AI is a little more believable than most shooter games. People on fire try to find water to douse themselves with, they will run to healing machines to try to heal themselves, and they generally act like they are trying to preserve themselves. They are all nuts, so some aberrant behaviour certainly fits, but they still act smarter than most games "smart" AI.
All in all, I think Irreverent (or 2K, or whatever they are calling themselves this week...) has a winner on its hands. I can only hope for a sequel or expansion.