Can be rough at first, but no matter the difficulty you can generally ignore it for the last 5 minutes- even the grey planets have enough fighters at this point to hold their own.
Just colonize everything early on at first and ignore the first couple of attacks, then recolonize reinforcing with your blues. Once everythings at 100% you can watch it for 2 minutes then leave.
A great diversion, but has one failing- Too luck heavy. Some of the groups of rocks you get just aren't passable; the rate of fall limits how much movement can be done. Get 2 groups with narrow 'safe paths' between them, and it can be literally impossible to get past both. In any given game, it's just a matter of time before you hit one of those. The scoring favors luck too- 100 distX10 rocks=1000 points, regardless of how the rocks came at you. 10 bumps on the bottom is the same as the grouping I mentioned earlier scorewise.
Recommendations:
Basic AI to ensure that the obstacles generated are passable with the in-game physics.
Scoring based on skill, such as the player ships distance from the passed obstacle (0 points for far, 1 for mid, 2 for close, 4 for REAL close?)
Something like this would give an incentive for the riskier maneuvers and put a higher emphasis on skill, and reflect that better in the score.
Might make for a good sequel?
Bug- if you collect any/all specials for one ship, back out to the menu in the same session without refreshing, and start with the other ship, you can then use all of the other ships specials on your new ship. When you purchase the new ships specials, they replace the old ones...
 "Solstice"){kind=icon}
 "Inversion"){kind=icon}
 "Star War 2.1"){kind=icon}
Since the 'Defend' option is new, the game could be to easy now. Try not to use 'Defend' but 'Attack' all Bombers manually ;) [edit: old version]