I liked it!
+ The graphics are basic, but the game doesn't seem to need better graphics.
+ The sound is pretty eerie, which I liked.
- Why couldn't I control the shooting of the space invaders?
- More upgrades except just more invaders would have been fun (such as shielding, lasers, choice between several space invader units with individual characteristics), because the novelty of the game wears off pretty quickly. Upgrades keep it fresh and keep players motivated.
- The title is pretty stupid, since I'm not defending anything at all. Space Evaders would've been a better choice if you ask me.