A neat, simple and fun 3D platformer - good job so far! :)
As BenFontaine & WigHz already mentioned, the contrast is quite low on my side too. Some more colorful environment would give the game some smoother and more polished touch. IMHO the coin pickup sound volume is also quite low, which confused me during the cloud sequence in the middle of the game (at least I wasn't sure if I collected a coin or not).
Overall, I had some fun while playing your game and was quite happy to see the boss :)