Thank you for playing my game and I'm glad you enjoyed!
In my initial idea for this game, you'd only score by collecting the gems, but I found that scoring was too hard and random if that was the only way to score, so I made killing enemies give points to spice up the game and make it more interesting.
By the way, you should try standing in a slot when it spins - it will spin all other slots relative to its spin direction, which is useful for navigating the map.