Not being familiar with any of the "Dead Space" games, or the first animated movie, I have nothing to compare this to, so this is all by what I thought of this 2011 animation.
"Dead Space: Aftermath" had a nice enough story and it was easy to follow. The story is about a small group of four survivors who are rescued after a tragic occurrence, but now they have to tell their stories to people who seem to have little regards for their well-being. As I said, not being familiar with anything prior to this animated movie, then I have no idea how true or far from the original plot lines this movie is. The storyline was nice and well told.
However, the solid storyline was brought down tremendously as they had opted to use various styles of animation and art styles. Most of these, sadly enough, were not in my personal liking, and thus it brought down the enjoyment of the movie for me. Especially the CGI animation, that was just horrendous. It looked like it was released before they had applied the finishing touches to it. In my opinion, then "Dead Space: Aftermath" would have fared better had they opted to stay with just one style of art and animation (in my opinion, the style they used when they were telling doctor Cho's story).
As for the voice acting, well then I think they really did manage to put together a good group of people for the voice acting. So that was really working out well for the movie.
I am sure that this 2011 animated movie is a great thing for fans of the games, but it failed to fully ensnare and captivate me. I am giving "Dead Space: Aftermath" a 5/10 rating because of the story alone, the different art styles and animation styles was the knife that killed it off for me.