I saw the 2D version. It was good (particularly the performances by Karl Urban and Olivia Thirlby), but....
The film was claustrophobic, with over 3/4 of it taking place inside a single building. This did not leave room for any exploration of the futuristic world of Mega City One.
There wasn't much humor. While the lack of Rob Schneider schtick was a good thing, the Dredd comics had a lot of twisted British humor which was missed.
While 3D may improve the action, it won't improve the above flaws.
Ted J. Kilvington, Jr.
"I still have that comic, only now it's in liquid form!"