Wow, multiplayer!!! Really neat! I played single player, but I will definitely come back later to try multiplayer!
Gameplay - I am sure my pizza was very, very cold by the time I delivered my first pizza haha. It took me a few tries - mainly because I wanted to bike faster, but I couldn't maneuver very well if I did. I'm totally cool with k being the only pedal button, but there were several times where I wished I had some sort of brake or backpedal button for when I knew I didn't have enough platform to make a jump and didn't want to start over again. I suppose in a race you don't really want to backpedal or brake anyways, but I found that the obstacle clearance was too tight to go faster. I replayed the level a few times after my first delivery to see if I could speed it up, but could only go a little faster, so this could be an area that would make the game really satisfying to play (or maybe I'm just bad haha). Since there's one fixed level, I thought having a final lap time display would be a nice touch. But if you're planning on randomizing the levels in the future, then I don't think a lap timer is that important.
Music was perfect (love the bicycle bell); the rhythm made me want to mash k immediately and as fast as I could, even though that move was not great for the first obstacle. The sfx were hilarious.
Art/Graphics were very clean; I like the style and the font. I know everyone's talking about coloring the obstacles - maybe you don't need to color them in, but slightly highlighting them might be enough to still match the rest of the art style.
Awesome job on your game!