Awesome Music: Pretty much the entire soundtrack. Listen to it here.
Disappointing Last Level: The final battle in the "main sequence" of returning the crystals to the Music Castle is long and drawn-out with marginally interesting attack patterns, and has both a visually misleading background that creates Interface Screwand a hidden time limit, leading to frustrating retries.
Goddamned Bats: The Ceiling Crawlers in the Luminous Towers levels. They love to dive-bomb you when you're not paying attention.
Oddly enough, not the Bombats from the Grassland Ruins levels.
The Dust Hill A Ghost, Helicopter Bouncing at Luminous Tower A and Collect a Path of Gems While Falling at Magma Falls B missions are given achievements at the game's website.