You can entirely circumvent some of the puzzles by clicking a rhombus immediately after another one, while it's still moving. Unless this feature is utilized in the full game by some sort of track on which they move slower, you should disable clicks while rhombi are in motion.
The tutorials could have been nice if they had taught you the rhythm for the end of 3-X. Having to decode a new rhythm while playing for the first time is not an easy thing to do.
Okay, when you go to buy extra slots, the price doubles after buying one. Why does the game wait to tell you until after you leave the shop and then go back in?
PRO TIP: the green minigame gives you plenty of time; get yourself to a safe place in the other games before paying any attention to it. To make the controls less confusing, pull your hand away from WASD during the time you aren't paying attention to it.
TO ALL OF THE PEOPLE COMPLAINING ABOUT PANTS COLOR:
to change your pants color, pause the game (with the spacebar) and click the sideways text that says "pants" located next to the blue box with the level stats and such.
 "Rhomb"){kind=icon}
 "A Dance of Fire and Ice"){kind=icon}
 "Ending"){kind=icon}
 "Clout: The Game"){kind=icon}
 "Elona Shooter"){kind=icon}
 "Ninja Hamsters vs Robots"){kind=icon}
 "Ninja Painter"){kind=icon}
 "Bit Battles"){kind=icon}
 "Crystal Story II"){kind=icon}
 "Notebook Wars 2"){kind=icon}
 "Multitask"){kind=icon}
 "LightSprites"){kind=icon}
 "Triangles"){kind=icon}
 "Feudalism II"){kind=icon}
 "SCGMD4"){kind=icon}
 "Fancy Pants Adventure: World 3"){kind=icon}
The game is designed to make timing not necessary, also it is designed to give player maximum freedom.