Shrek is a hard one to review for me. On one hand, the animation isn't very good and the story is basically a mean-spirited Disney parody complete with fart and belch jokes. On the other there are some funny moments and if it were not for those funny moments Shrek would surely be labeled Drek by me and would get a low rating.
My biggest problem with the film (and most of the Dreamwork's films) is that it seems to rely too much on big name celebrities, crude humor, the parody of Disney films and fairy tales (which Enchanted did much better in my opinion. It was a lot funnier and it was not mean spirited) and "entertaining the adults" (aka "HA HA! They said 'ass' in a kid's movie!").
Also, I thought the animation in the film was very sub-par for a big budget CGI film. Especially on the background human characters (who looked like mannequins) and Shrek himself.
In conclusion, I laughed at the film and I didn't go through hell like I did with Horton Hears a Who! (which basically uses the Dreamworks formula... badly...).
However, I cannot label the film as "great" as most of the people I know do.