1) A cast of guys that normally don't have lead roles in movies. For example, this is the first time I've seen Bradley Cooper in a lead role. I've seen him in other movies such as Yes Man and Wedding Crashers, but he really made a name for himself in this film.
2) We don't see what actually happens to these guys during the night. We get to relive the mystery of what happened to them over a period of two days. It enhances the comedic effect and surprises the audience more.
3) The pictures at the end credits.
4) The baby that looks like Carlos, but is named Tyler. The sunglasses fit the part.
5) The tiger in the bathroom. I had no idea it would belong to Mike Tyson.
I don't want to ruin the rest. Go see it!