In regard to Shrek 1, it's a good movie, actually thought-provoking as well as entertaining. I'd say it's worth the buck or two to rent it, if you have nothing else to do, or if you are entertaining Marissa.
She may have seen it already and might want to tell you everything that is going to happen. Let her.
But you won't need to see the first movie to be entertained by the second. I was only commenting on how well they handled introducing a new character, Puss n Boots, especially since so many here at Amy's are GaGa over kitties.
Animation has certainly come a long way. Consider: They made Joan Rivers look youthful. I think all of the voice talents had fun with the script, and working together.
When Marissa spends the night, we go to bed with some sliced apples and a movie. The apples have become a habit. She used to tell me she was hungry and wanted candy. I convinced her that she would rather have an apple. : )
Next time she spends the night, I will rent shrek 1. She will love telling me all about it but if it is like when she reads me a story, she won't follow the author's script!