I love both the visuals and the collaborative aspect of this game. It's fun and it was well executed. You've managed to blend the characters and the scenario majestically. I also like how you introduce the controls in-game, in the beginning, and I appreciate the decision to make a single health bar for the team.
For a future iteration, I suppose the game would benefit from adding a non-fixed hud that indicates where the goal is (for the level 1), since you don't really know what you're supposed to go before reaching the top. I would also change the particle effects from the items on the top. They are going up, so the player can barely see it. Instead, I would maybe highlight the outline of the item or add some aura to it. After all, those are just details and this game is high-quality enough.