A sextuplet of zombie movies?

How many Resident Evil movies are there supposed to be anyway? Brian and I just finished Resident Evil: Retribution, and it ended on a cliffhanger of sorts. We have always enjoyed these movies for some reason, and sit together quite contentedly to watch them whenever they're on, or there's a new one out. So, we got the newest movie released on DVD, and happily sat to watch it, only to be full of "meh" at the end.
Okay, I'm gonna check; it's driving me crazy.

There are FIVE Resident Evil movies, and this one, as I said, sets up a sixth. These things are like Rocky flicks at this point. Or, more aptly, they are a virus that keeps multiplying.
That's not to say that we won't watch the next one when it comes out. But probably it will be viewed via Netflix (as this one), because when it ends on an ambiguous and loose-ends image, the last thing the theater needs is Brian and I calling out for a finish to this already.