Froot Lupes is a fantastic collab, simply due to the fact that it's a joke level that transcends itself due to the high quality of it's design, you can see the effort that went into it.
I think that one of the best aspects that a level can have is when you can perceive that the creators had fun and enjoyed making it, the bosses, animations and backgrounds are fun due to this, making it fun to play, with the different tasks you must do for the coins an added challenge.