definite improvement
I played the first iteration of this and felt like it had very little time and effort put in to it. Now that I see where you are taking it I am much more confident in voting at least a 3. Some tips if you're going to continue:
1. Some sort of storyline. I could see this being the basis for a decent defense game.
2. Cannon upgrades between levels.
3. Different types of shots.
4. Different enemy types and an amount of damage taken.
5. Don't let bad scores get you down. After seeing this much improvement in that short of time I feel like you can do something good with this.