Wedding Crashers became an instant classic because of its mix of fun, sex, quirky characters, and light romance. Everybody from womanizers to romantics can find something they like in it.
Each persona on the set has its quirks and speak their own dialect. The settings are luscious, the music excellent, the editing impeccable, the women beautiful, the complex dialogs fast paced, and the story engrossing.
There are only 2 things I would say pushed the envelope too far. 1) The fact that Vince Vaughn's character has some serious issues concerning food. It just doesn't fit well with the rest. 2) Will Ferrell's character is a tad too odd, although it fits within the story, it doesn't mesh well with the others, especially with his last appearance.
Watch it, you'll have fun.