That's half the $59.99 retail price of the package, and it's also $10 cheaper than Black Friday, when most retailers were offering the bundle for $39.99. Amazon is only offering this deal on the PlayStation 4 and Xbox One versions of the Legendary Edition; the PlayStation 3 and Xbox 360 versions are available for $39.99.
The Legendary Edition includes the original Destiny game plus three expansions: The Dark Below, House of Wolves and The Taken King. It's a great entry point for people new to the game, since The Taken King — Destiny's latest expansion — costs $39.99 on its own. Plus, The Taken King is necessary to access all content from Year Two of Destiny, including free limited-time events like the ongoing Sparrow Racing League.
For more on The Taken King, read our review.