The main problem that you notice straight away is that all of the characters were born and raised in the Uncanny Valley. In fact, they'll probably get married, grow old and die there too. The voice acting is fairly poor too, which doesn't help matters. Add into the mix some of the craziest floaty CG hair in certain scenes and we're not off to a good start.
But stick with it. The opening half hour is pretty chock full of action. A plane crashes, zombies attack and zombies get shot in the head. All good stuff. The next half hour gets bogged down in exposition and 'really not that much happens' territory though. It all picks up again for the last thirty minutes with explosions, mutants and slow motion bullets a-plenty. Pretty much a game of three thirds.
Real actors were filmed in a motion capture studio as a basis for the animation. Their facial movements were also recorded when they spoke their lines. The actor that played Leon (Paul Mercier) must have been wearing a plastic Liza Minnelli mask for all the expression his face shows. Not even a flicker of a smile. You can probably tell I'm not that impressed with the technology but the fire effects and explosions are gorgeous. Fire is notoriously hard to do with CG (way easier for pyromaniacs) but they have done a great job here.
If you can suspend your disbelief with the characters' blank stares and put up with a slow middle third then there's a half decent action film to be found. Worth a watch if you can get it cheap and way better than any of the live action Resident Evil films. But then most things are. Even anaesthetic-free DIY tooth extractions.
If you like this you could also try:
Vexille, Appleseed Ex Machina.