I had played this some time ago and don´t know why stopped at 5-1. A few days ago I sarted playing again and now I understand why this game gets so much praise in GAF. Once you get accustomed to the controls (my mind kept telling me to keep Y pressed to run like in Mario games and forgot to press jump to bounce on enemies) it plays so beautifully...Getting into the zone and blazing through the level bouncing and rebounding on everything at high speed is really awesome and speaks loduly about the awesome level design. I also love how puzzle pieces are found through exploration, while KONG letters are more based on skill and you have to get them every time you die, they work as an indicator that you´ve mastered the level and they´re always in the main path, so getting them everytime is just a matter of skill and no backtracking or time-consuming actions are required.
I´m currently at the volcano boss in world 6 but have also started replaying older levels to get everything.
One question, what does the DK sign stand for next to the level´s name in the sumary? Puzzle pieces and KONG letters are clear, but many (maybe all, I just noticed it) of my levels are showing that DK sign greyed out.