Its seems like Shrek 3 has been getting average reviews in the US according to this on the BBC website:
"The third instalment of the successful Shrek movie series has received mixed reviews from critics in the US.
Film industry bible Variety said that while many characters were still enjoyable, the series was showing "signs of encroaching middle age".
The Hollywood Reporter said the film lacked the wit and bite of the original and the makers had "gone to the well one time too many".
DreamWorks' first two Shrek movies made