I played a lot of this recently. I honestly haven't had the patience to finish the whole game in one go, it's brutal!
But I really enjoy the graphics, the music, and I love the cartridge design:

It was definitely Taito's response to the success of Rockman. It's very similar, with the main difference being your weapon is a boomerang instead of the mega buster.

There's a good game there... You just need to be patient. Instead of localizing it outside Japan, they almost remade the whole thing, improved it a lot, and renamed it "Power Blade" for the NES.

It's a nice cartridge to have in the collection. I wish I had the box and manual too. The manual looks amazing and the box is plastic, I assume like the Mega Drive ones.

Have you played it? Do you have it in your collection?