Donkey is constantly singing or humming in the film and the audience both enjoys this, and understands when Shrek is annoyed by it. .
Lord Farquaad is the "villain" of the fairytale, banishing the fairytale creatures and attempting to create a "perfect", but rather dull kingdom. However, the typical villain role is taken out of context as we find out that Lord Farquaad is in fact very short. Several jokes are made about his height and this makes him seem less menacing than the typical villain. The audience will not empathise with or relate to this character, and his character is not fully developed in the film.
Princess Fiona's character begins as a typical fairytale princess; very ladylike, well-mannered and well-spoken, but as the film progresses she becomes more three dimensional, revealing a more relaxed, more modern, maybe even more "real" side to her personality. Women are most likely to relate to her later in the film, where she becomes more similar to "the modern woman". In instances such as when Fiona encounters Robin Hood, he is very rude and treats her like an object, making sexual comments and openly staring at her. Many women will have been in a similar situation and can therefore empathise with her.
There are several different layers of humour in the film to appeal to different viewers. Firstly there is "toilet humour". This is most likely to appeal to children and men and appears throughout the film. "Toilet humour" is quite a basic, crude form of humour, making jokes out of bodily functions. A good example of toilet humour is when Donkey and Shrek were approaching the castle and Donkey said, "Ooh Shrek! Did you do that? You gotta warn somebody before you just crack one off! My mouth was open and everything!".
A lot of jokes in the film are also made by taking scenes from other popular films out of context, for instance, when Fiona was singing to the bird (similar to a scene in "sleeping beauty") and the bird exploded.