I am a big fan of tower defense. I was bored with this one in the first level.
Graphics: the backgrounds and enemies look great, but my units look flat and boring. The animations for my units are so quick they seem fidgety.
Gameplay: There are many enemy types, but they are not introduced to the player, you just have to go to the pause screen and mouse over them. You should start with a few unit types and introduce more over time. Most TD games show the upcoming wave or waves on the screen as you are playing. I don't want to click a button to look at what is coming up. The number of waves is too high, especially for the first level. The units and spells should be introduced more slowly.
Story: a sense of progression helps to draw the player along. It doesn't have to be great; just some small excuse about why I am here, what I am defending, and why the enemies want to get through.
I initially gave it 4 stars, then changed my mind and gave it 5. The music is well done, the writing is entertaining. I think the artwork in the story scenes could use some polish, though. It just feels rushed and "wobbly". I ended up buying the full game and soundtrack. I enjoyed the first 20% enough to pay $5 to finish it. Here's hoping that the rest is at least as good! I also appreciate that the full version comes with access to the Windows, Mac, and Linux versions.