Defender was the pack-in game for the Entex Adventure Vision. I have to say, the translation is great. All the action that made the original arcade game a hit is here to make it very addictive.
Defender screen-shots and sound samples.
Defender ROM image
My favorite strategy is to collect all the humanoids and keep them with me. It takes a little practice, but it's definitely worth it since the landers are a heck of a lot easier to kill off than the mutants.
The opposite strategy also works pretty well after you have racked up 8-10 smart bombs. You kill off all the humanoids and then start smartbombing all the mutants. This makes for some pretty quick rounds, that is until you run out off smart bombs.