This is a 4D maze that's presented in 3D rather than 2D like the other one found in the store. The markers for surfaces I had already visited were not entirely clear to me. I love the subtle color scheme, I think I just did not fully understand where the markers are placed. Overall, very nifty.
Update: I get it, the markers are for faces I *haven't* visited, duh. I forgot to mention, the algorithm for determining which portal I mean to roll through is VERY good. Most apps I've tried are frustrating in that regard--this one gets it every time, even from awkward angles and even when there are overlapping portals.