This is an interesting take on the traditional tower defense type theme. With all the different worlds to choose from, it's clear you put a lot of work into it. There are many different character choices to launch. And lots of options to discover.
The music is pretty good. It's a bit repetitious, however. Maybe not the exact same tunes... but the same style. So that could use some variety.
The graphics are highly pixelated, but they are done in a consistent style for both the scenery and the characters. So that's good. However, I found the level of pixelization a bit too coarse. It was difficult to tell what the some features were. Fortunately, you have a mouse-over feature that displays the name of items. But still... I feel the graphics are just too rough. Perhaps if you used a smaller display window.
Speaking of display window, there's no reason to run this full screen, with a smaller display inside. Windowed mode would be much better. Plus that would allow easy closure. As it stands now, I had to use the Task Manager each time I ran this. Esc would pause the game. But P would not close it, as advertised. That's VERY unfortunate when players can't easily quit the game -- especially in full screen mode.
There's lots of worlds to choose from, so that's a nice feature. I prefer the worlds where everything is on the same screen. It's cumbersome to have to scroll around to see the action as the characters move along the path and interact. Just my preference.
But overall, this is fairly good. Not my favorite genre and style. But except for the full-screen issue (and exit problem), it should appeal to fans of this genre.