Fun game! I liked the background art. The music is decent enough too. I also like kittemple's suggestion to add a bit of background animation randomly appearing like the cow appearing or something. I think this game has potential and could be a 4 with some reworking, it's definitely fun to play, I got to level 11.
Hey. Some suggestions: make a start menu or something that makes it clear what you are supposed to do to win, it is a bit unclear how the game works. The actual gameplay is mildly amusing, with some sound or additional features this could be a fun game, I almost gave it a 2 without any changes except for the lack of a start menu.
Cool idea! Maybe make the rockets a tad faster in the beginning and make it clearer how many hits you can take before you die... I still had most of my monuments left when it said I lost.
 "Vicious Explosive Circles of Doom"){kind=icon}
 "My First Flash Game!"){kind=icon}
 "Frantic Frigates"){kind=icon}
 "Scarecrow. Battle for the Harvest"){kind=icon}
 "Simple Tower Defense 0.5"){kind=icon}
 "Snake"){kind=icon}
 "Monument Protector"){kind=icon}
Thanks! I'll keep that in mind for the next upgrade or version. :)