While the plot is mostly straightforward, there are some oddball bits that don't make much sense. For example, at King Harold's funeral, why is the soundtrack "Live and Let Die"? (Unless it is an oblique reference to the demise of John Cleese's recurring role in the James Bond franchise?)
The quest to bring Arthur back to Far, Far Away seems low risk with little at stake besides some rather heavy handed efforts to establish a mentoring relationship between Shrek and Arthur. Mr. Merlyn (voiced by Eric Idle) isn't all that funny and serves mainly as a convenient plot device. One wonders why the supposedly mercenary Puss in Boots hangs around, since his role is pretty much reduced to being second banana to Donkey.
Back home, Fiona and Queen Lillian lead a jailbreak, but they and the other captive princesses don't really get to do much before being surrounded and dragooned into Charming's over-the-top revenge setpiece.
I don't know--it just lacked spark. And this franchise also seems to have "jumped the shark" most particularly since today's paper announced that not only will there be more "Shrek" movies (number 4 already in development with core cast signed on) but that there will also be a half-hour made for TV "holiday special." Groan! Ogre babies are cute (and I'm surprised I haven't seen dolls--"Skunk Cabbage Patch" anyone?) but they could well be to the "Shrek" franchise what Ewoks were to "Star Wars."
Whether we bother with any more of these will depend upon reviews.