Nice little game especially the graphics.
The gameplay however feels very repetitive, it would of been nice to have some ennemi variety and ramping up the difficulty when the core goes up. I personally qui the game after 400 score because it was too repetitive and not challenging enough (might only be me though). The sudden death mechanic is a really nice idea but it makes the game way too easy, you can also abuse the sudden death mechanic to reunite your 2 little buddies together and basically play only 1 character wich takes away the whole fun of the game.
Overall a nice looking game that unfortunately is a little too repetitive and has a lots of small flawes in it's design you can abuse, hope this helps you improve the game :)