The RE franchise has always had a weird interrelationship between the games and the movies; though both follow roughly the same plot of a viral outbreak, there are many, vital discrepancies between the two; though many game characters reoccur in the movies, the movies are never explicitly about the game characters; though the games touch on many emotional subjects surrounding a viral outbreak, the movies are almost exclusively about Milla Jovovic's kung fu.
The plot of the games revolves around four main characters (Chris, Jill, Claire and Leon) and deals with them coming to terms with a mass outbreak of various viruses (the T-Virus, and las Plagas, to name the main culprits), which have been engineered by the company they used to work for: Umbrella. The games follow the characters in their various attempts to thwart Umbrella, close down their labs, and generally save the world.
The movies were an accidental success; director Paul W S Anderson only intended on shooting one movie, which was supposed to be a tie in to the games, a la Stargate (different stories existing in the same universe, never interacting). He wrote a script full of Alice in Wonderland references (hence the main character's nickname), and turned the movie into an exhibition of his wife's ninja skilzz. The movie did not go down well with game fans, but the rest of the world loved it, and so the RE franchise was born, and Anderson bailed out of the director's seat in order to concentrate on the script, and so the story continues. The next movies loosely followed the game plot, with a few familiar characters showing up, but after 5 movies the plot is still centered around 'Alice', a stand in for the gamer.
The fandom is ultimately split down the middle: those who love the games and get all antsy about the existence and worldwide popularity of the movies, and those who love RE regardless.
In summary: Resident Evil is not a zombie story.
The fifth movie is set for release in September (October in the UK, boo hoo) and sees Alice living a dream life, only to be woken up (by none other than everyone's fave game character Ada Wong) and told that everything has been constructed by Umbrella in order to test the T Virus on Alice. So, to back track, everything that happened in movies 2-4 was fake, Alice was placed inside the 'dream world' at the end of the first movie by Dr. Isaacs. This has been my theory from the beginning, and I'm mega thrilled it's right, not least because it makes such a good story.
Alice says that Umbrella created a world in which everyone she's ever known appears (so Jill, Claire, Chris, Carlos - all game characters, who -- in the 'real world' -- Alice encountered through her job as head of security at Umbrella, hence how she knows Angie, who is the virus developer's daughter). This is where my theory gets deep:
Alice's 'dream world' is a meta representation for the process of gaming, i.e. in order to test the virus, Umbrella put Alice in stasis and constructed this world in which she interacted with game characters, slayed boss monsters, and generally progressed through the levels using a power beyond her own mind - the virus, or a gamer controlling her, because we learn in the 2nd movie that the virus takes over her actions (for example, how she is forced to fight Matt, who is also being used to test the virus).
So that's the 5th movie. In movie 6 (which Anderson has said will be the last in the franchise, but he said that three movies ago) it's reported that all game characters will be returning (which means Chris and Claire, who are absent from movie 5), and that there will be a resolution to all outstanding storylines, mainly the odd ending to the 2nd movie, where characters who have already died (Jill, Carlos, LJ and Angie) return to rescue Alice from the Umbrella lab. All of this is speculation, but it's speculated by Milla, and being married to the writer is a credible enough source.
What I think will happen, again, is that Alice will once more awaken from her 'wonderland' (i.e the game) and in some finite way shut Umbrella down once and for all, and rescue Chris & Claire from their respective games also. Jill, Ada, Leon and Luther have already been liberated from the game, and Carlos and LJ (while still existing in Alice's game) have been killed in the real world. It sounds like the Matrix, only fundamentally isn't, because Capcom have been setting this up since the first game in '96.
(I generally don't care what happens in the movies, as long as there is at least one scene of interaction between Jill and Chris, the original game heroes).
Also, it'd be pretty cool if, at the end of the final movie, the old-school Resident Evil 'game over' logo flashes up. Just sayin'.