The Family Stone is a bit of an awkward family drama/romantic comedy combination. The plot follows Everett (Mulroney) as he comes back home for Christmas to introduce his new girlfriend Meredith (Parker) to his family and to ask his mother (Keaton) for the family wedding ring so he can propose to her. His youngest sister Amy (McAdams) already hates her for reasons that are unknown to me--and presumably everyone else watching the movie--and plays mean tricks on her so the rest of the family will share in her distaste. Everett's brother Ben (Wilson) feels bad for her and tries comforting her, but she feels so harassed that she invites her sister Julie (Danes) to join her. When Everett picks Julie up from the bus station, he falls head over heels for her. There are a few more family members and plot points that I'll let you discover firsthand if you choose to watch this, but that's the basic framework.
Despite the few comedic moments in the trailer, I didn't find the movie as a whole to be very funny. It also wasn't very uplifting or feel-good. A lot of what happened just seemed outright mean and/or depressing. Throughout the movie I felt like it was all a big inside joke that I didn't get, but in the end all was explained satisfactorily with subtle hints instead of over-the-top verbalizations. And the final shot was terrifically bittersweet. All the technical aspects were competent, but nothing truly impressed me. All in all, see the movie if you liked the trailer or the actors, but I don't think this movie is the one to change your mind about the genre.