We’ve given this Bangai-O Spirits a little air time in the past. I’ve picked it up at Target for $15. (They have a cheap DS section now, $10-$20.) From Wikipedia: “Bangai-O Spirits is a side-scrolling shooting game with free-scrolling levels that extend horizontally and vertically. The player controls a robot with the ability to fly, but is still affected by gravity. He has seven weapons to choose from, and can perform melee attacks using a baseball bat or sword.”