I gotta say, all three 'threequels' I have seen this year (Spiderman, Pirates, and now Shrek) I have been disappointed with. Spiderman 3 was the most disappointing.
I enjoyed them all, don't get me wrong. I just felt they could've been better.
I saw Shrek 3 yesterday, and I thought it was good, but disappointing. I don't think it was the storyline that needed much fixing up, I felt it was the comedy that was a bit of a let-down. Similar jokes to the previous movies, and not really anything new to add to them.