Sign up to receive each week’s Playlist e-mail here! Also check out our full, interactive Playlist section. HELIX (iOS) BY MICHAEL BROUGH This shoot-’em-up is less of a bullet hell and more of a thumb ballet. Arc your preferred digit in graceful concentric circles around jellyfish and moonrocks to make them explode in dazzling showers of sparks. There’s no tappa-tappa-tappa, just a slick slide across your iDevice’s LCD. Please don’t blame us when full mind-meld mode sets in and you miss your bus stop. Perfect for: Geometry warriors, thumb-twiddlers, your daily commute. Playtime: Best played in bursts of 20 minutes. LATE NIGHT DRIVER…