Sisters is a typical American slapstick comedy, The type you just leave your brains behind and just watch for the fun of it. Nothing fantastic except for a few funny scenes, and its pretty forgettable. Sisters is the kind of movie you just switch on something while you have your lunch or dinner which is what I exactly did.
The casting is pretty decent. Tina Fey and Amy Poehler who have done a few movies together and Saturday Night Live for awhile now have really good chemistry with each other. Them as sisters is pretty believable.
Like I said its a typical American comedy so don't expect nothing but a few laughs here and there even though some of the scenes and plot is incredibly stupid.
Worth watching on a weekday or just wait for cable. You are not missing much.