My impresions, I hope to not be too harsh and give you some ideas on how to improve:

• Sadly I don't think the game worked correctly: The "player" cube moved very very slow, the "collectable" cubes spun very quick and the cube was not able to jump over the first obstacle. If the game was working correctly and the player must do anything else, then it's too obscure and you need to somehow teach the player what he/she is supposed to do.
• Unify aesthetics: A realistic background does not match the abstract looking graphics, nor does the font used. If you are going for cubes, then make the background out of cubes and choose a more blocky/squarish looking font.
• Do everything with purpose, ie: why are the collectibles laying around randomly? You can give the player a "feels good" start by sorting them in a line to be easily collected while also showing him/her the way. Or, if you want the player to navigate around the platform so he can try the movement controls and take a look around, four collectibles in a square pattern would suffice.
• Transitions will hide small loading times and give your game a more polished feel. 
• If you don't have graphical assets you can still add some eyecandy with particle effects (remember that you can use custom geometry with the particle system, creating cubic particles) and "animating" the cubes. Consider stretching the player cube as it jumps and squashing it as it lands, for example.
  
  Hope this helps, good luck!