I only beat the first level, but I guess I'm just bad at using a mouse and a keyboard at the same time. It was fun, and I liked the sound effects (the music felt a bit repetitive even though I could tell there was some variation). Saying the player is a collectible picked up by another player seems like a nice way to not take the theme too literally. And yeah, I didn't get to see there and back, but I'll just assume it is as you say.
I liked the scoring system, but maybe instead of showing the score for a certain amount of time and then switching to the next level or to the game over screen, you could have shown the score and put a button below that took me to the next level or to restart the current one if I didn't beat it. And maybe show the score faster, waiting for an animation is annoying (just like it would be annoying to not have time to see the score if you're bad at reading).