I played alone, and it was very nice!
More fun than I thought it would be, to be honest.
I liked the little touches, like how the music stops when you stop; and how the carriage warps humorously as you stuff up.
Things I would change:
1) some sort of score system or lose condition - it feels like there is no reward for playing well;
2) centre the action more with some look ahead - playing right at the edge of the screen feels awkward; and
3) smoother up/down camera movement when going over hills.
Good job overall, though!
:)