It's a nice start, and I like the concept. I'll definitely be interested in purchasing the full game once it is a bit more refined. Some things that could be improved:

1. More variety in the scenes - I never like to compare (it's the thief of joy) but a similar game that predates this one had multiple different types of endings you could hit, as well as non-standard game overs that made the game a bit more compelling.

2. More balanced gameplay. Once you get beyond a certain point, it becomes a bit too much like rock-em-sock-em robots, unless you play on lower difficulties.

3. More unique sprites. Many feel straight lifted from the base packs.