Really not sure where all the super negative reviews are coming from, I guess just people who consider themselves too good for this type of raunchy and silly humor. Sisters is about two immature women refusing to grow up, adults reliving their teenage years, and that is what is so funny about it. It is over the top sometimes, but comedy is supposed to be different from reality. If everyone was behaving like mature adults in this movie, it would be boring and it would last 15 minutes. "Oh, mom and dad, you're selling the house? Well awesome I hope you get a good deal, see you at Christmas..." Now I will admit there were a few misses with this movie, the end dragged on a little too long, but overall I enjoyed all the characters and most of the jokes were great.
