I didn't think this was as much of a downer as I'd heard it was going to be, if that makes sense. I also didn't think the plot held together all that well -- I was kind of hoping for some sort of explanation on what happened to the fertility rates, and why animals seemed to still be being born. I did like the implication that there were more animals around because people wanted to fill the void left by the lack of children. But it bothers me that I might just be making that up because the backstory was left out.
I was worried about the cinematography because the movie uses that "dystopian future" color palette that usually accompanies artificially sped-up action scenes that have a lot of frames taken out so people flip around and kind of strobe, but it turned out they were just using the palette without the other gimmicks. In fact, I loved the camerawork, although it was so flashy that I spent some time trying to figure out how on earth they shot certain scenes. There was also one scene that felt a lot like a videogame, specifically Half-Life 2 or possibly this one X-Box 360 game where you run down a city street while things blow up around you. I don't remember its name, but the demo was pretty good.
It wouldn't have been my favorite movie of 2006, but it probably would have been fifth or sixth on the list.