Hrm, I'm not sure I like the fact scenery changes randomly. I would recommend 3-4 sceneries exchanging in a preset pattern (like road, forest, ice, city, road, forest, ....) each day (not each time of the day change). With the current difficulty I'm not sure many would reach day 5 so there would be a sense of progress. Also, did you notice the player's bike blending with the road in the forest? Maybe change the bike's color in the forest to dark grey.
Noticed one bug. Clouds are drawn over the score.
My suggestions:
* retro sounds and/or perhaps non-retro soothing background music
* preset scenery change
* maybe slower increase of difficulty
* high score save feature
* fixed number of digits score display (like 001, 020, 123, 999)
BTW, did you implement max difficulty?
Also, did you experiment with pseudo-pixel movement for the bike? I think this would give more options to player when dodging.
Played 4 times. My top score: 276