Some people I know would give this a higher rating and fuss over the fact that I didn't give this movie a 5. However, I am not as emotionally invested in the characters or the movie as some people I know.
Sometimes you are just in the mood for a classic. You already know the character types, you already know the plot, and usually you know the plot twists and where they will occur. A movie like Serenity gives you a sense of stability - you know you will like it because you have seen it before. The reason you go? You go to see a new version of what directors, producers and actors have know works for years. You go to see the new wrapping of an old and well thought out gift. Serenity is a movie where you will laugh, sit on the edge of your seat in suspense, pump you fist while river demolishes an army of villains, and squirt a tear when a beloved character bites the dust. A guy can cheer during the action scene and his counterpart female can stereotypically cry on his shoulder during the more emotional moments.
I saw this movie; and I agree with you. It was a good movie, but some (ahem- Brandon) are wayyy too emotionally attached to it. I enjoy this film (even though I wouldn't have thought I would). I appreciated the cheap humor and innuendo's, as well as good prevailing over evil. But I wouldn't rate it a 5 either.