I didn't think another Shrek movie was necessary but the recent success of Shrek Forever After proves there was a Shrek void out there I clearly wasn't aware of. Like every other movie being released, it's in 3D, and I can't say the effect brought anything to the movie. It certainly didn't compensate for the distraction of wearing the goggles. Not to say the movie isn't wonderfully animated. Like the other movies in the series, the animation if imaginative and colorful and helps move the story along - a sort of re-working of the It's a Wonderful Life idea where Shrek gets a chance to see how things might've turned out if things hadn't've turned out as they had.
The usual characters are there doing their usual things and that might be might biggest criticism of the movie. If you liked the characters before, you'll like them again. Essentially a re-tread of what's gone on before, there's nothing new here, just another installment in the series. A nice way to pass the time but not a must-see.
(The best thing about the movie? The preview of Toy Story 3D. I counted three laugh-out-loud moments in the trailer, more than I had in the entire Shrek movie.)