The interface and usability of SUDOKU is great, and the ability to mark possible options for each box is easy to use and quite helpful; I also like the quirky awards after completion of each puzzle - a shovel, milk cup, ocarina, etc...but there is some memory leak in SUDOKU that begins to cause extreme issues with response and usability, and the phone quickly heats up to the point of freezing, while draining the battery at a speedy rate. Not sure if it is the ads or just going between filling the squares and marking the viable options, but the issue is quite annoying. I also think that the freezing hinders the timing of completing each puzzle, so the stats and ranking cannot be accurate for each person. I continue to play one or two games a night as a distraction, but the freezing makes it tough to want to play more than that. Still, this is probably the best this app interface I’ve seen.