It seems like the enemy AI can deal very well with the player attacking 1 planet, but fails when you attack lots of planets at once. In the end there was really only one tactic - pick the toughest enemy and send all your ships at all his planets at the same time. I enjoyed it for a while, but I think there needs to be more attack options to make it more strategic.
That was good fun! Didn't think much of the challenge mode though - it got a bit repetitive. It would have been nice to have had a different challenge on each world. I noticed a bug with the rock bosses as well - If they get frozen during their rebuild phase they can't be hurt until the ice thaws, which is a bit annoying. Still, I enjoyed it :-)
it's fun but the UI is horrible. Don't put upgrades, achievements and levels all on different top-level menu trees, it makes it a pain to navigate. You should be able to go straight to upgrades or achievements from the level select screen.
It's possible to exploit the "new wave" button as you can call for new waves at a faster rate than the creeps can be added to the level. Once you have a basic defence you can just spam the button until you have enough cash to make a mega tower, then build it before the tough creeps get into the level. Using this tactic on survival I was able to get to wave 5000(and counting).
I'm pretty sure that 22 and 24 can't be solved with logic alone. Seemed like I had to guess one tile in each of those levels. The rest were fine, though. Nice art, too!
it's pretty fun, but I started to dislike it after the speed up. Having to jump in so early in a lot of the levels made it more about reaction time than good timing. If the levels were a bit wider I think I'd enjoy it more. Great work nonetheless, such a cool concept.
 "Hyperpath"){kind=icon}
 "Puzzle Monsters"){kind=icon}
 "Wild Heroes"){kind=icon}
 "Bubble Tanks Tower Defense 2"){kind=icon}
 "NoNoSparks: The Ark"){kind=icon}
 "Space is Key 2"){kind=icon}
 "The Last Frontier"){kind=icon}