Droid Assault is fun because of attention to detail. It feels good to fire the weapons, it's rewarding to watch the enemies explode. It's just very polished shooter that I had a lot of fun playing.
The usual gamification nonsense that seem to be implemented in every single flash game ever made is present and correct, but that doesn't take away from the pure fun of shooting stuff. Droid Assault absolutely nails that part, and is a game worth checking out as a result.
Droid Assault [Armor Games]