... The first Shrek film was a genuine four-quadrant hit: kids loved it and so did critics, but so did snarky young teens like myself at the time, who appreciated its upending of the films we'd grown up with. The second Shrek film spawned spinoffs like this Simon Cowell-starring American Idol spoof, and it was downhill from there. ...
I don't think "downhill" is the right term. The third Shrek was considered a disappointment (40% fresh on Rotten Tomatoes) and Shrek 4 was not the money spinner everyone at the studio hoped for.
But maybe, if DWA concocts a durable story, it's time for Shrek 5. It only seems right, since multiple sequels are now the thought for the day, every day. Plus the ogre is now an official internet phenomenon.
Added to which, sequels on top of sequels on top of sequels are now the law of the land.