It's set after RE4, but it's ment to set up for RE5.
Interesting this came up, I'm a huge RE fan and own every game (and sadly, every movie). To be honest theres a lot of people out there that hate the films but the question I ask is: Would you still hate it if it was named something different?
I theorize the answer would be "yes", mainly because the film franchise isn't that bad, only it was a different take on the game series. Infact the first film has very few references to the game series. Off the top of my head I can only thing of a few. The red queen, the crows, the STARS logo at the end of the film, and some camera angles.
I know some people are already thinking I've missed some major ones, but the mansion isn't referenced as the Spencer mansion, and the hive is only loosly based on the underground umbrella base in RE2. But anyway, thats the references I've seen.
On topic, I really want to watch this movie!