I just picked this up and had a quick blast on it - it looks fun and is really addictive (and has a good co-op mode too), but I have a question:
How do you 'clear' planets in single player mode (and is it the same in co-op)? Do you have to get a certain score or is there a point where you've killed all the baddies and then that planet is done?
I couldn't find anything about it in the manual and I haven't 'cleared' a planet yet so thought I'd ask
Good game though!