The world three overworld has an inescapable area in the top left, those 3-4 levels MUST be completed LAST. I loved the shareware version growing up, and I don't spending some money on it now, but it's a bad deal. It's just more of the same, and with more of those dumb invisible platforms and pixel-perfect jumps. They're still not too hard, but there are a lot of gotcha-areas which force you to reset the levels. I recommend the first episode, but not the other two.
