too much advertising dude!
A good basis, i can't knock you for trying, but I have a couple of improvemets i think you should add in that'll really make this game something.
1. When i complete the level or fail and get a game over screen, any remaining UFOs don't disapear which makes the game feel like it hasn't been polished enough.
2. I couldn't help but notice that when playing the game, there was a 'clock' at the top of the screen but time was not passing, which just seems weird. maybe along with adding that in, it would be good idea too put in a background that gets lighter and darker depending on the time of day.
3. My last thourght would be to add in some upgrades for the player: Faster movement, faster rate of fire, more damage, more cannons, auto fire cannons, more weapon type, elementle damage, faster xp/money gain ..... and the list goes on, try to add as many as posible.
The game was good if it was your first though but I would still recomend improving. You can never get to a point where you have a 'perfect'game, it's impossible however, the closer you get the better
Keep up the good work,