Is it just me, or are the single player levels, even the most difficult ones, fairly easy to go through.
I feel like they made the marble have such tight controls, that as long as you are careful, you can easily zip through the levels.
In 2 hours, I completed all but 4 of the 60 levels, and most of them are under par. I think it might take an hour or 2 to complete the advanced levels all under par (15 left, 4 of which I have not attempted)
I just find this to be a bit elementary in difficulty, nothing challenging unless you have limited previous experience in games.
However, it is super fun, I love zipping through levels, it is one of the more relaxing games I have ever played.