Youve made a great game! This is just the type of free games i like - simple to understand but challenging to win nice looking strategy. The graphics are nice and sound is good too. One of the best free games ive ever played.
My only issues were sometimes with the controls of the units and wih the need to point at avery asteroid to find out hows the battle going on - if you have 5 battles going on at the same time, ure just trying to make sure you have greater numbers in each of them. Something like "battle status indicator" at the asteroids would help a lot.
Also the color glow around asteroids should be more bright, at certain levels of zoom theres almost none. And some of the colors (i think two blue or orange ones) look almost identical. Sometimes its hard to tell if ure controling the asteroid or not.
The "plant" button also needs some resizing of the active "clicking" zone, i cant tell you how many times ive clicked on this button and it just deselected the asteroid.
If it is possible, some AI improvements and difficulty settings would be great too. Some special units or different asteroids would make the gameplay more rich, but should be optional - like in HARD mode or so.
The vitality/str/speed thing is interesting, but so far, ive been almost ignoring it, except when capturing first 2-3 asteroids.
Dont make it too complicated, its brilliant in its simple system. Focus on the controls and make the vit/str/speed stats more usefull.