Not sure if one mentioned this. I really would like to have a function to save current game progress in a certain stage. y'know, most players including I have a pretty hard time completing one stage in a short amount of time, especially those in the late game. I usually cannot spend this large chunk of time on completing one stage and I had to start over every time I restart the game. This is really annoying and preventing me from going through further level. (I bought the game for almost a year and have stuck with those levels for almost the same duration)
You can save my world by posting a save button for each stage so that I can choose to use the saved game or start over. (Or just start with saved game automatically when a reset stage button is available)

Besides, there are also some tiny problems I would like to mention here.

1. I would be more than happy to see a "back to stage selection" button than simply a quit-to-main-menu "quit" button.

2. the description for the achievements of "watching something flying over the screen" is really vague and I just completed a few of them randomly. I cannot even finish the rest on purpose even I actually saw a panty flying over and no achievement recorded for completing that. Really, really confusing.

3. C'mon, offer me an option to play in window mode.

4. when a stage is activated and I have to switch to another active window, the game is still running in the back. When I click my mouse, it still activates the character. Please get this one fixed. An auto-pause function would do it.

5. Nah, that's it for my question. this one is simply for complaining how hard it is for me to complete the whole game. [facepalm