3D glasses aren't all that different from sunglasses (though, please, never try to wear them as if they actually are sunglasses). You put them over your eyes and they make everything darker, which can be a real challenge for a movie that's either not compensating for that, or a projector not set up for 3D properly. Even though a lot of Dredd takes place in the dark-- there's literally a shield above the building blocking out all the sun-- the brightness is never an issue here. Looks like shooting in 3D also helped them avoid the many pitfalls that can come with it.
Brightness Score: 5/5
The Glasses Off Test
This isn't so much a test of whether the 3D is good as how "much" 3D there is-- if you take off your glasses in a scene, the more blur you see, the more the images are likely to pop when you put the glasses back on. Dredd is a gritty movie that, even in the flashy sci-fi scenes, isn't all that interested in going overboard with the 3D. Though there's a subtle blur in pretty much every scene, taking off your glasses will make it clear how different this is from the more extreme 3D films-- the blur is barely a factor, and the 3D barely is too.
Glasses Off Test: 2/5
Bad 3D can induce nausea, whether because the various planes of action don't match up or the simple fact of straining your eyes through 3D glasses makes your head hurt. The 3D in Dredd has so little impact that it's not really a problem, but beware of everything else in the movie-- there's a lot of blood and a lot of intense slo-mo sequences, which may turn your stomach for reasons that have nothing to do with the 3D .
Health Score: 4/5