Manipulative tripe
I am passionate about hating My Best Friend's Wedding. This is the worst movie I've seen, even beating out Eraserhead (at least it's experimental). I will not forgive a director who cares more about manipulating the audience than crafting a story.
In a nutshell, the Dermot Mulroney and Cameron Diaz characters are nothing more than plot devices; they are totally flat characters who act in completely inconsistent ways, simply to keep the audience guessing which woman will be selected.
If you cannot tell a story with consistent characters, you're telling the wrong story or using the wrong characters.
This could have been a decent movie if they'd cut down on the "suspense" of who the Dermot Mulroney character would marry and instead focused on unconventional relationships and defining family.