The Day does have one flaw and that is the script. While the story is simple to the extreme it is efficient enough as it set its events in motion leading up to the very bloody siege. So far so good but the problem is that most of the characters are thin to the extreme, though well acted. Not all of them, Ashley Bells Mary is quite an intriguing one but apart from her and Shawn Ashmores Adam we never get to know any of them other than basically their names and the fact that they knew each other before the apocalypse. This makes it somewhat hard to root for any of them but thankfully the movie is tense enough and filled with a shitload of graphic violence that it never becomes a major problem. And for the gorehounds out there you will have plenty to enjoy. Mostly cgi but well done, nothing ever struck me as looking odd or particulary artificial.
The cinematography is another thing that might be a weakness or even a strength, depending upon your own preference since it almost totally devoid of color to ensure maximum bleakness. Some of the scenes feel almost black and white, like back in the old days when you collected dupes of uncut horrormovies and received one that had been copied so many times that there were only tiny flickers of blue and green at times. I kinda like it, it suits the movie.
So what I am saying here is basically that you shouldn't go into this expecting anything that will blow your mind away, just a exciting and very violent post apocalypse movie. The original script had zombies instead of cannibals which tells you a lot about what the filmmakers were going for. Good, gory and colorless fun.