Of note, this is a movie. It will not scare the pants off of you like the games can. Understanding that it is not the game makes the film easily enjoyable.
The CGI is VERY well done and the English voice acting leaves little if anything to be desired. The storyline is simple and recurring characters are portrayed faithfully. The fight scenes are choreographed very well.
Leon seems to have more quips in this film, but those are forgiven in the light of everything else. Thankfully, he is starting to show a bit of weariness in his plight. JD steals the show for a short bit without detracting from the mood of the film. Ada is ruthless and manipulative as ever. All in all, a fun ride.
You do not need to have seen Resident Evil: Degeneration to enjoy this film, though I would suggest you see it anyway as it is a great film in its own right.
For fans of the video games, there is a treat to be had that is not on the cover.
This film, as well as Degenerations, are considered to be canon whereas the travesty known as the live action films are not.