Needs different difficulty setting, more interesting enemies and levels, towers should be more balanced, better music, more levels, boss waves, and an in battle main menu button. The positives far outweigh the negatives, 4/5 highest I've ever rated a beta.
All the songs really create a wonderful atmosphere that you would not normally find in any flash game. The first was was superb but this just blows me away. I for one think you deserve the spot as top rated game.