Another way of looking at this movie
I liked this movie quite a bit, and was surprised that I liked it because it got mediocre reviews when it first came out. I finally caught it on DVD when my roommate bought it.
Here's the thing, and after watching Modern Romance, the Albert Brooks film, I have a feeling that the tone, which is this bickering, somewhat painful, embarrassing, and downright unsympathetic/mean-spirited back and forth between Aniston and Vaughn especially, was done on purpose. A method to the madness; modern romance can be awful and not pleasant to watch, and I think a movie like this captures a sort of cynicism that is not unfounded. I have problems with the movie, namely the ending, I liked the director's ending a little more but it's not as humorous as the theatrical version I guess.
I completely understand why people would dislike the movie, but I just have a feeling that the nastiness was done to jab the audience a little more than usual, to get them a little uncomfortable so as to make a point about how relationships when not dealt with in the best manner (although breakups, there doesn't seem to be any good that comes out of it during the actual break anyway) can ruin people for a while. I think it's just kind of a counterpoint.
Now if you really want to get unpleasant, I'd suggest Funny Games. THAT is a really, really twisted ride.