Not quite perfect, but close enough for me.
I'll start by saying that I've had a blast playing this game over the last few days. It's not easy by any means, but the gameplay is so simple that there's no frustration over learning unit types or getting used to the interface. What this ends up meaning is that the difficulty of the game makes it a challenge, but not a chore.
Now, onto the few minor things I would suggest for future improvements:
The first thing is the music. There wasn't any. The ambient background noise was well done, but it's a poor substitute for some good tunes. Tossing music into the background would do wonders for this game's atmosphere and replay value.
Secondly was the storyline. It's a fairly generic basis for a story, but we're not asking for 100% originality here. If you could flesh out the backstory a bit more, make it a bit more personal, that would probably be the largest single improvement this game could use. It would be ideal to have multiple campaigns, but let's not get ahead of ourselves.
All in all, I've had a blast playing it so far, and I don't plan on stopping anytime soon. Keep up the good work!