Some part of the game are really hardcore, it's a very very challenging game, I like it very much but it can be really frustrating.
I spent a day to get in world 2 !!!! after I ended stage 1-8 I had to get back and forward to collect a bunch of stars in the previous stages, from delivery and no crash, very challenging indeed. Btw, world 2 is great, very different from world 1, from what I have seen so far