I was really excited to see this movie - hoping that the comparisons to the original Hangover movie were apt. The movie started out really slow to me (I felt the setting up scenes were too long), but then the movie reached its stride about 20 minutes into it with the engagement party scene.
The laughs were coming pretty strongly after that point. I have to admit, I adore Chris O'Dowd from his work on "The IT Crowd" and so my affection for him may color my enjoyment of him, but I thought he was a great character in the movie.
But the movie is really Wiig's, and she is, at times, adorable, horrible, and strong. I really enjoyed the last act and now the final song has been stuck in my head since then!