This app has an excellent geometry engine and setup, reminiscent of Geometers Sketchpad if you ever played with that. Solving the problems is great fun, and heck, sometimes the constructions are so challenging, I am happy to get 1 star and just complete the problem. Or I do a basic construction that I thought I had mastered but havent earned 3 stars, and discover there is a better, more efficient way, like how to construct a perpendicular in only 3 steps, which happens early on. Also, many problems need to be done twice by different methods to get all 3 stars. I prefer this version to Euclidia 1, because of the structure, though, I do play both versions. It is interesting how there is a slightly different progression through the problems/puzzles, and this version has more problems and asks you to solve more of the problems/challenges in more than one way. And although I am currently up to Epsilon, there still are plenty of problems/challenges that I need to perfect, most notably, I still need to go back and try to 3 star that inscribed square in Alpha level. Frustrating but good frustrating. Beautiful and sublime.